Throwback Thursday: AR-15 .223 vs Mil-Spec 5.56mm Chambers

.223 Rem vs. 5.56mm Nato

When it comes to AR-15 .223 vs Mil-Spec 5.56mm chambers, what are the biggest differences? Most people do not know. They say, “I think you can shoot both kinds of ammo through either one, right?”

Then, they buy an AR-15 and start to get more educated. Frequently, they later have regrets they did not get the AR with a chamber they wanted because they did not know what to ask.

We are going to cover the major options in AR-15 chambers, including Mil-Spec chambers and the benefits of each. I am going to limit this to .223 Rem. and 5.56mm chambers and will address ARs with other calibers, such as .308 (7.62×51 NATO), in the future.

There are three types of chambers in the M16/M4/AR-15/MSR family of rifles, but most people think there are only two.

  • The first is the Mil-Spec 5.56mm chamber, which is used in the M16 and M4.
  • The second is the .223 chamber, the most common chamber in AR-15 rifles, although you can get AR-15s with a 5.56mm chamber. (Why you would want that is very interesting and I go into that in detail below.)
  • The third is a .223 Match chamber, which is used in AR-15s by serious, competitive AR-15 shooters.

.223 Rem Chamber

First, let us cover the most common AR-15 chamber: the .223 Remington chamber, commonly called .223 Rem or just .223. Most AR-15s also come with chrome-lined chambers and barrels.

It does not make sense in the manufacturing process to only have the bore (barrel) or only the chamber chrome lined, so if you read a spec sheet that says an AR has a “chrome-lined barrel,” you safely may assume the chamber is chrome lined as well.

.223 chambers are made to SAAMI (Sporting Arms and Ammunition Manufacturers Institute) specs, not Mil-Spec, so the chambers are slightly tighter and smaller than Mil-Spec 5.56 chambers.

Normally, that is not a problem since the most plentiful ammo available to civilians is .223 and not 5.56mm. But many people buy ARs with .223 chambers because they do not know any better, and then they find out there are drawbacks to ARs with .223 chambers.

Drawback #1: The Myth of Using 5.56 mm Ammo in a .223

The first drawback to .223-chambered ARs is the myth that you can shoot 5.56mm Mil-Spec ammo through it. Manufacturers that print the two calibers on rifles and in rifle manuals synonymously further perpetuate that myth.

varmageddon .223 remington ammo
Nosler Varmageddon ammunition is a premium line of .223 Remington ammunition.

You can shoot 5.56 through your .223 chambered AR-15—but you may regret it.

Since 5.56mm Mil-Spec ammo is loaded hotter, it has higher chamber pressure. Built to SAAMI specs, not Mil-Spec, the .223 chamber is ever so slightly smaller than a 5.56 Mil-Spec chamber. So when you shoot 5.56 in a .223 chamber, the case cannot expand as much as it would in a 5.56 chamber.

Therefore, a couple of things happen with varying frequency. The most common is that you will blow primers; that means you will have the primer blow back into the receiver, which decreases reliability as it rattles around in your receiver or on top of your magazine.

You also will experience an increase in failures to eject the spent cases because the case has expanded so much from the hotter load in the smaller chamber, and you may not get the case out of the chamber without putting a rod down the barrel. Shooting Mil-Spec ammo through a .223 chamber also may crack your upper receiver. This is less common, but still happens, and is potentially dangerous to the shooter and nearby people.

So you can shoot 5.56 through a .223 chamber, but it is highly inadvisable, as both are not equally safe for your AR-15.

Drawback #2: Heavy Bullets

The second big drawback to a .223 chamber is shooting heavier ammo—77 grains and above. This is the preferred bullet weight for national match shooters and snipers. The problem is that those rounds are slightly longer than lighter AR ammo, so the projectile is sticking slightly farther down the barrel when you chamber the round.

The problem becomes very obvious when you try to eject the heavier round from the chamber without firing it. This happens because the heavier projectile is slightly longer. On occasion, the rifling grooves may grab it when you try to eject it. The result is that you pull your charging handle back and the case comes off the bullet, spilling unspent powder on the receiver (and your magazine if you did not remove it first).

As it ejects, you are left with a projectile in the barrel, and you will need a cleaning rod to knock it out. Then you will have a mess, and it is not fun—especially when you are on the firing line at Camp Perry competing for the national championships.

.223 Match Chambers

This brings us to the .223 Match chamber. Most .223 Match chambers are not chrome lined. The biggest difference in .223 Match chambers is that the rifling does not begin as quickly, so you do not have the problems referenced above with the case coming off the projectile if you try to eject a live round from the chamber.

This is the preferred chambering for serious competitive shooters who like to compete at the national level, such as at the NRA National High-Power Long Range matches and CMP (Civilian Marksmanship Program) matches at Camp Perry, Ohio, each summer.

5.56mm Mil-Spec Chambers

Then there are Mil-Spec 5.56mm chambers. These are always chrome lined in the M16/M4s for the military and typically are for their semi-auto AR-15 brothers. The 5.56mm Mil-Spec chamber is slightly larger than a .223 SAAMI spec chamber because the Mil-Spec ammo is loaded hotter and has higher chamber pressures.

Benefit #1: Use Both .223 and 5.56 Ammo

So the supreme benefit of 5.56 chambers is that you can shoot .223 ammo and 5.56 out of a 5.56 chamber without reliability or safety concerns. That gives you the flexibility to take advantage of the great military surplus ammo bargains when they are available.

The downside is that, at greater distances, some shooters think they will see a decrease in accuracy shooting .223 ammo through a 5.56 chamber because the chamber is ever so slightly larger.

I think that is arguable. I know what you are thinking: “How much decrease in accuracy?” and “At what distances does it make a difference?”

I believe that 95% of shooters will not see a measurable difference, except at extreme distances for which they may not have the training to shoot effectively anyway. Remember, when it comes to shooting, most of the time “It’s the Indian, not the arrow.” Remember, I am talking about shooting .223 ammo through a 5.56 chamber only—not 5.56 through a 5.56 chamber.

Benefit #2: The 5.56mm Chamber Has a Slightly Longer Throat

The second benefit of a 5.56mm chamber is that it also has a slightly longer throat/free bore area. In simpler English, that means that there is more space between the projectile and the rifling. Remember when I explained what happens when you try to eject a live round when it is 77 grains or above from a .223 chamber (not a .223 Match chamber)? Well, that does not happen with 5.56mm chambers because of the longer throat.

Benefit #3: Availability of Ammo

The third benefit of having a 5.56mm chamber on your AR involves a little paranoia but isn’t unfounded (although I pray it never happens. Some of my prepper fans out there believe there may be martial law one day in America, which would include an attempted disarming of Americans.

5.56 NATO Ammunition
A box of 5.56 NATO ammunition.

That is what Hitler did, so it is not unimaginable.

In any case, nobody can argue that, in an extended time under martial law, you might only be able to get ammo by stealing it off the back of a Humvee—if you do not get shot trying to do so in the first place. I would want an AR-15 with a 5.56mm chamber so you can shoot military ammo through it without added potential reliability problems. And remember, you will still be able to shoot .223 ammo as well.

There is a way to ream out a .223 chamber and make it 5.56mm. I have heard that it is easy, although I have never done it. You might be able to find the reamer, but if I wanted that, I would have it done by a reputable gunsmith.

What Chamber Should I Buy?

So now you may be thinking, “This is really confusing; just tell me what I should get.” It’s a common question when debating .223 vs Mil-Spec 5.56mm.

If I could only afford one AR, I would get one with a 5.56mm chamber.

I also would not trust the labeling on the spec sheet on the manufacturer’s website or even in the owner’s manual that any AR-15 is 5.56mm or .223/5.56mm. I have tested ARs lately that claim, in writing,  that they are both.223/5.56mm. I’ve seen it on their website spec sheets and in the owner’s manual that came with the AR. When I called the manufacturer and asked if the chamber is 5.56mm or is it .223, the manufacturer tech help person dismissively told me it is both.

I stuck to my guns (forgive the pun) and said, “It can’t be both; either the chamber is SAAMI spec .223 Rem. or the chamber is Mil-Spec 5.56mm; which is it?”

Then, from one USA manufacturer, I received the response, “Well, it’s a .223 chamber, but you can shoot both through it.” Another USA manufacturer told me, “I can’t put you through to a tech person, but you can email me, and I will forward your email.”

I did email that customer-service person who could not answer my question, and I confirmed receipt of my email and that the rep forwarded it to the “appropriate person.” That was more than a week ago. As of the time of this writing, I still have no response. I will not own or recommend any of their ARs for the foreseeable future.

Until next time, I will share with you what Ron Mida, one of my shooting mentors always told me: “Shoot Straight!”

The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (270)

  1. I used to argue this with people who repeated rumor & myth. I have never seen an AR chambered for true 223, and I wish there was. Think about it: every AR is 5 56, but nearly all ammo is 223. You get the option of shooting either, but at a cost of wasted potential. I would prefer an AR that uses the full potential of the 223. Mine are now Wylde, but even that is a compromise.

    As for the misleading marketing, I just tell people that ammo marked as both is actually 223. Rifles marked as both are 5.56.

  2. Just purchased S&W MP 15 Sport II 5.56
    The barrel has 223 etched near the muzzle. Can I safely fire 5.56x45mm rounds in this weapon???

  3. So I recently bought my first AR, I wanted a 5.56 chambered rifle but got a Match Target .223 because I got a good deal. Might be a stupid question but can I just replace my bolt carrier with a 5.56 bolt carrier and start shooting 5.56 or are there more changes I would need to make?

    1. NO.! First, the problem is not the bolt. The 5.56 chamber has a longer throat which allows for the longer bullets that are usually loaded in the NATO ammo. Second, the BCG you would end up with won’t be any stronger than the match grade BCG you already have. Third, the BCG you have was specifically fitted to our barreled action to get “target-match grade” accuracy. Replacing it will ruin that matchup without gaining any benefit. Fourth, the only reason to shoot the 5.56 ammo is because you have access to economical qualities of it.

  4. Hey I just bought a Remington ar556 and it says I can spit both so my question is since it’s an ar556 does it shoot 556 or 223s or both

    1. I do not know of a Remington 556. I am guessing you meant Ruger 556. If that is the case, yes it will shoot either .223 Remington or 5.56 NATO. ~Dave Dolbee

  5. “There are no differences between the specifications for 5.56 and .223 Remington brass.”

    I have to question the validity of this statement. Every thing that I’ve read states that NATO 5.56 brass cases are thicker in the case wall, perhaps specifically to withstand the rigors of being fired thru belt fed weapons. NATO 7.62X51 ball cases are also thicker in the case wall.

    Reloaders are specifically cautioned, in publications, to never put the same powder load in a NATO case that they may have worked up in a load for .223 or .308 cases as that would or could result in a catastrophic event.

    1. Interesting comment. It is also contrary to anything else I have heard or been able to find out with my own research. So I have to ask you to prove it. Back up your comment with some supporting documentation, or at least some links to reputable publications that show support to your opinion.

    2. Hitler disarmed the German Jews or any Jew in Germany. I’ve never read anything addressing the disarmament of Aryan Germans. He may also have disarmed Catholics and homosexuals, whom he imprisoned, but I have no knowledge of that. I believe he enacted a death penalty for any Jew found with a firearm.

  6. Here is the actual math between caliber – millimeter and vice versa.
    Calibers are generally described in hundreths and thousanths of an inch (i.e. 30 cal, 50 cal, .223, .265 etc)
    The standard conversion accepted throughout the world is 1 inch = 2.54cm where 2.54cm = 25.4mm because there are 10mm in 1cm.
    (i.e. 30 cal = 30/100 or .30 of an inch further if you multiply this by 25.4 you obtain the result of 7.62)
    Regarding ammunition some of these expressions do get truncated.
    Here is the odd thing about all this: .22 directly converts as 5.588 and .223 as 5.6642. If you work this in reverse 5.56 directly converts to 0.2189 which when rounded is .22 or 22 caliber. To the articles point 0.004 inches or 4 ten thousanths of an inch may be imperceptible to the human eye but where chambers and cup pressures are concerned these differences are great. The chamber is designed to keep the cartridge from expanding and even at 0.004 of an inch it makes a great difference.

  7. My AR has the chamber size stamped on the barrel (5.56 NATO 1:8). I don’t know if all manufacturers do that or just mine. That is confirmation in my mind as to the size.

    1. That makes hell of sense. Pressures lost on the 223 cartridge, means less distance, maybe less spin. Thanks for pointing that out.

  8. Great answer! Most people have NO idea there’s any difference between the two rounds, much less the chambers.

  9. I notice a few people say that they prefer the .223 to the 5.56. My wife and I bought each other the S&W AR15 Sporters for our anniversary several years ago. I like it so much better than the Ruger Mini14 that I had 2 of over the years. Both of the S&W’s are 5.56. I reload for most all my guns, but when I can buy a box of 1000 rounds of Federal surplus 5.56 for $250 that tells me I’ve got the right caliber for my rifle. Add the fact that I can still shoot .223 from it accurately. I’m happy with our choice.

  10. I experienced a punctured primer when I first fired a surplus 5.56 from a bolt action Remington 223. I was not wearing shooting glasses (for the last time), and I thought that I had lost eyesight in my dominant left eye. After I got the soot and gun oil out of my eyes and off my face, I put on my glasses and tried it again, thinking that it was just a fluke from the cheap ammo. It was not, and after three shots and three punctured primers I quit shooting. Moral: shoot 5.56 from a 223 chamber at your own risk, but don’t forget to wear your shooting glasses.

  11. Thanks for the detailed information, I knew the basics of this situation before buying my “budget brand” AR. My rifle was certainly represented as having the .556 bore. The only missing information in your article is the actual dimensions of each bore. Easier than contacting customer service is to simply measure your own gun. If you could tell us the different sizes I could measure my rifle faster than typing this post. ( I’m tool and die maker and have my own pin gage set) let us know the sizes and we can check at the store before buying. Thanks -Dave

  12. You cover, very effectively and thoroughly, the AR15, however know one covers, or mentions, the Ruger Mini14. Can you address this fine rifle as well??

  13. This is all BS, every word of it, if any part of it was real the insurance companies and the personal injury attorneys would be all over this, if there was any chance, even the slightest chance, that someone would be injured by shooting a mil spec 5.56mm round through a gun stamped .223, the gun manufacturer would be shut down and the problem would be fixed, but, you see the problem doesn’t exist. I could compare this to older guns chambered for .30-06, the ammo manufacturers will only build .30-06 rounds to the original pressure specs, so they are not responsible for blowing up older guns and hurting someone, the same is true for .45 long colt, none of these companies want to be sued, IF THERE WAS ANY CHANCE THAT SOMEONE WOULD BE INJURED BY SHOOTING A 5.56 MIL SPEC ROUND IN A GUN CHAMBERED FOR .233, THE GUN MANUFACTURER WOULD IMMEDIATELY CALL BACK ALL OF THOSE GUNS AND MAKE DAMN SURE THE GUN COULD HANDLE THE 5.56 ROUND. THIS HAS NEVER HAPPENED , SO, YOU NOW KNOW THAT ALL OF THIS CLAP TRAP IS STRICTLY BS.

  14. Great information! I own a AR-15 Competition H-Bar, the barrel is stamped CMP 5.56 NATO 1/9 HBAR. I also have a Ruger Mini 14 from the early 80’s marked .223 and a Remington 700 BDL heavy barrel marked .223. Going by the markings I gather that I can safely shoot .223 or 5.56 Mil Spec through the AR but probably should not shoot it in the other two?

    I took about a 20 year absence from any type of hunting or shooting due to a career change. I’m now retired and trying to get back up to speed.

  15. I agree with your article. I only have one criticize. It’s a common myth that the Nazis disarmed the citizens, but it’s not true. The Weimar Republic had much harsher gun control laws than the Nazis. The Nazis just made use of the existing legislation. It’s argued that these gun control laws made it easier for the Nazis to assume control with less resistance, but that’s another topic.

  16. I wonder about this in bolt actions. I’ve considered a bolt action in .223/5.56 for ammo availability and prices. Is it safe to shoot 5.56 in a bolt action chambered in .223?

  17. I have no desire to steal 5.56mm ammo off the back of a military Humvee…I’ll stick with the Remington .223 chamber…the ammo is much easier to obtain….If and when push comes to shove…I’ll steal an AR16 off the back of a military Humvee along with the ammunition it shoots.

  18. The way I understand Wylde chambers is, they are mil-spec, but modified to not lose accuracy when firing .223. My almost “bargain basement” Eagle-15, an Armalite AR-15, has a Wylde chamber. And, guess what, Wikipedia has a good article on Wylde.

    1. Ruger Mini-14 barrel is stamped .223 but is a Wylde chamber so can safely fire 5.56—difference in round dimensions between .223 and 5.56 not trivial and not without consequence when attempting to fire 5.56 from any other .223 marked firearm. Manufacturers cover themselves by cautioning to always use ammo for which firearm is labeled and no other…otherwise all bets are off.

  19. There is another variation on the .223 or 5.56 chamber. It is called the Wylde chamber. The throat is elongated and slightly over-bored to allow use of bullets weighing up to 90 grains, being set at maximum cartridge length without touching the lands. I think the free-bore is slightly enlarged also, just in front of the case mouth, tapering to a tight fit just in front of the ogive of the bullet, which would give pressure relief while keeping the bullet properly aligned with the bore. This modification allows the chamber to be SAAMI spec in tightness while allowing the use of 5.56 ammunition safely.
    I can, however, tell you that there is nothing wrong with the military M16A2 in 5.56 where accuracy is concerned. I am retired Infantry and used to instruct basic and advanced marksmanship. With the right rifle and a good ‘lot’ of ammunition, the A2 and the A3 are capable of sub minute of angle accuracy with 62 grain ball ammunition. I have shot 25 meter targets for zero while conducting training with open sights where the three shot groups all hit the dot in the center of the zero target’s circle and made one ragged hole using open sights, and have used (unauthorized at the time) scoped A2’s to shoot 100 meter groups that were inside an inch. Unless you’re shooting Bench Rest competitions, the accuracy differences due to the (very slight) differences in chamber dimensions between the 223 and 5.56 will be masked by other environmental factors, provided good ammunition is used. Mil-spec ammunition is not match-grade ammunition, so don’t go by how accurate it is in your rifle. Keep in mind that each lot only has to meet military requirements for accuracy, which is nowhere near match accurate. Your mil-spec chambered rifle may be extremely accurate, but your mil-spec ammunition may only be capable of 2 1/2 inches at 100 meters from a test barrel. And foreign ammo for sale as surplus may not have passed even that requirement. For example, I have fired Turkish ammunition in 7,62X51 (.308) that wouldn’t print inside 5″ at 100 yards in one of my rifles.
    If you want a match accurate AR in 5.56, the chambering won’t affect the accuracy of the rifle significantly. The ammunition used will. So will the type of barrel, rifle manufacturer and the trigger mechanism. First, buy the rifle from someone like Fulton Armory, who makes very high quality rifles in AR10, AR15, M1A and M1Garand configurations, with accuracy guarantees. Then either buy premium ammunition or reload for match accuracy. Also, while the short barrel M4 configuration is a specialty rifle, and of little use past 250 meters, so stick with the 20 to 24 inch barrels.

    1. Your comments were spot on.
      However – the original article is as misleading as they always are.
      There is no difference between a .223 & 5.56 cartridge. Honestly – there are over a half a billion reloaded cases sold annually made from brass picked up everywhere from military bases to local shooting ranges – who/what would sort these out for the reloading process safely? The .223 was designed to shoot bullets from the 30 – 50 grain range thus shorter OAL needing a shorter freebore. The 5.56 is the same cartridge but loaded with 55 to 77 grain. 99% of military loads are 55G or 62G (M193 or M855) which were designed with a longer freebore = the 5.56 chamber. The pressures are the same for the same load/grain bullet – SAAMI measures mid case and the military (NATO) measures at the neck. Just as with a hosepipe – there is more pressure at the pinch point so the NATO round measures higher and appears “hotter” to people who are drawn to the bigger is better philosophy.. There have been countless double blind tests with both rounds with chronometers and no one has ever been able to consistently identify which round they were firing. THIS is the differece – SAAMI does not test the same way NATO does so they will not comment on using the 5.56. The danger of the 5.56 is that it will most always have a heavier grain bullet which is longer and when you chamber it in the shorter .223 chamber there is less freebore range (length from tip of bullet to the rifling) and thus could build up to unsafe pressures. This would only happen with 77G+ bullets. If you are shooting M193 or M855 you can shoot all day long with no worries – i have done it with tens of thousands of rounds along with my shooting buddies with chambers labeled with dual compatibility and nobody has ever had any difficulties – blown primers – etc… this is the same rifle range cowboy stuff people love to “educate” the newby’s on. Go with the 223 wylde – shoots all available grain bullets safely and more accurately than the 5.56 at longer ranges.
      BTW – a commercial 223 & 556 cartridge hold the exact same volume water and weigh the same and have the same OAL empty – where would the difference come from?

    1. Every thing that I have read about chamber difference is the “throat lead” is longer and a siight different angel. But nothing about the chamber being actually larger. If you look up “cartridge” dimensions for 5.56mm and .223 Rem., you will find they are the same numbers. All the chamber dimensions I have found are for the .223 Rem.
      Where can we get the actual chamber dimensions for the Mil-spec 5.56mm?

  20. Counting your dedicated match chambers, there are then four chambers in this family. 5.56; .223; .223 match & .223 Wylde.

    My rifles are 5.56 from Daniel Defense and two M4 uppers with 1:8 Wylde barrels–an 18″ & 20″.

    The Wyldes will safely accomodate NATO 5.56 & civilian .223. Above 77 gr you may need to feed single rounds as the OAl may exceed your magazines limitations.

    I’m sure that you are aware of all this, I post it for those that do not.

  21. Great info for the owner/operator of an AR type platform who is unaware of the ammo differences.
    However, at the risk of raising the ire of the Lawsuit Gods, would it be possible for you to actually Name NAMES of the offending platforms? Those who balk at specifying or just down right REFUSE to say because, in fact, THEY DON’T KNOW what they are selling for whatever reason?
    Public “shaming,” if you will, has been shown to be VERY effective at creating behavioral changes in today’s business world and I believe it would be used to good advantage in this instance as well, my Good Sir.
    You’ll be accomplishing several (GOOD) goals.
    One, telling the manufacturer they’ve been “outed” and they NEED to come clean and,
    Two, letting your loyal readers know which manufacturers we might need to avoid like the plague because, for all intents and purposes, they are, very nearly, putting OUR safety in jeopardy by their lack of knowledge or downright bullheadedness and/or ignorance. Even if it is only their Tech Support folks.
    See what I did there? 😉
    Anyway, I would personally appreciate knowing who those Bird Turds are who are so reticent and cavalier about failing to KNOW their business and putting some possibly unwitting customers or innocent bystanders at risk of injury.
    Thank you for your efforts.

  22. Thanks Jerry. I’ve been trying to explain this for years, but as you stated, the manufacturers perpetuate the myth. Now I can just refer them to your article. By the way, 5.56 is all I have outside the Grendel. I have not noticed any significant difference in accuracy up to 200 meters. After that the hotter load of the 5.56 begins to show itself. With much greater penetration. And slightly tighter groups. Again thanks.

  23. That’s why I prefer “Bolts”! I have a “Frankenstein” 98k Mauser, chambered in 8mm-06 with a Japanese Type 38 Barrel “Rebored to accept a .35 Whelen (9.1×63.34mm)…

  24. Thank you for a thorough explanation, it’s so hard to find articles where they actually discuss the topic, so thanks, good info.!

    1. What about the Wylde Chamber. This chamber design is said to be constructed to allow safe firing of either 5.56 mm NATO or .223 Rem. My Springfield AR-15 has such a chamber.

    2. I have the ARmalite 15 and the barrel says 223 Wylde and that is exactly as you described it – shooting either bullets without problems

  25. Picked two Stag Arms AR 15 lowers recently. What is your opinion on 5.56 Stag uppers? Your article explaining the diff btw 5.56. & .223 was very informative. Thanks.
    Army and Law Vet

  26. What is your opinion about Stag Arms uppers? Recently, I purchase two Stag Arms lowers, but waiting to complete both ARs. I been researching uppers for some time, including the Crossroads Gun shows. Your article about 5.56 vs .223 is very informative. Stag advertises 5.56 chambers:
    “Action: Semi-auto direct impingement
    Chamber: 5.56 NATO – this rifle will also shoot .223
    Twist Rate: 1/9 button rifled
    Muzzle Device: A2 flash hider (Stag Arms Compensator on post ban models)
    Barrel: 16″, 4140 steel, chrome lined, government profile, manganese phosphate coated
    Handguard: Free float Diamondhead VRS-T handguard
    Upper Receiver: Forged and mil-spec 7075 T6 aluminum with type 3 hard coat anodizing and a picatinny rail on top
    Bolt Carrier: Standard bolt carrier with a manganese phosphate coating”.
    Army and Law Enforcement Vet

  27. it is my understanding, according to RUGER, their MINI 14 has a WYLDE chamber specifically for all the reasons mentioned. it came in the MINI, before RUGER introduced their AR 556 MODEL.

  28. This is easy. If you buy a 5.56 chambered gun, you can run both the 5.56 and the .223. If you buy a .223 chambered gun, you CANNOT run 5.56 ammo in it. They create a lot more pressure as they are loaded per Mil specs. You’ll end up with split cases, possibly injury to you and damage to your gun. I’ve heard some people say or comment on here you can shoot a 5.56 in a .223 chamber. Simply not true! Period! Now there are some guns that have a Wylde chamber. They are designed to run both safely. So if you want to shoot both calibers, then get a 5.56 gun, or one with a “Wylde” chamber. It’s that simple. Anyone that says you can safely shoot 5.56’s out of a .223 chambered gun, is ignorant and most importantly WRONG. Just Google it and you’ll se I’m 100% correct!

    1. @ Derek – Wow! Great job basically copying everything that was written in the article, and then taking credit for it. Don’t hurt yourself while trying to reach around to pat yourself on the back.

  29. It’s a never ending question for folks new to the AR15. Here’s the straight shot: Forget what it may say in a description about what a particular AR15 will shoot caliber wise. You must look at what’s stamped on the barrel to be sure. If it says 5.56, then you can shoot both the 5.56 NATO AND the .223. If it says only says .223, then that’s all you can shoot. The 5.56 NATO creates higher pressures and requires more headspace. It’s not safe at all to try and shoot a 5.56 in a chamber only marked only .223. You can damage your gun and yourself! Now, if the chamber is labeled 5.56/.223, you can also shoot both rounds safely also and be fine. Typically, these are called “Wylde” chambers and a good barrel to have. A bit less common. Again, If you want a 5.56 make sure it’s stamped on the barrel!! Here’s a link to the “Wylde” chamber at the end just in case you’re interested. Good luck and have fun choosing your new gun! There’s so many to choose from now! A lot of good ones for $1,100-$2,200 range. Don’t believe anybody that says it’s fine to put a 5.56 in a .223 only chamber!! If you have any doubts, go straight to the mfg. and check with them first, email, phone, etc. “Wylde” chamber link: (

    Just paste it into your browser if it doesn’t create a link when I send this to you.

  30. I’m in the market for an AR chambered in true 5.56 MIL spec, and this double label crap has been driving me nuts. ASSHOLES, the lot of them. If the chamber isn’t 5.56mm Mil-Spec then don’t even bother putting 5.56 in the description! So much for integrity. Looking at the Rugar AR-556 at the moment. I miss the days you could pick up a decent SKS for $75. Damn.

  31. Actually the 5.56 has a thicker case: Military cases are made from thicker brass (to keep from splitting the case), which reduces the powder capacity due to higher pressures. This difference in the point of measurement can account for a difference of pressure measurement of 20,000 psi or more. Your gun needs to have a NATO or MIL-SPEC chamber, which features a longer leade. The Wylde and Armalite chambers are the exception. They designed these two chambers to handle both 5.56mm and .223 equally well. Conversely, if you have a 5.56 stamped on the barrel, you can fire both the 5.56 and the .223 equally well.

  32. There is a tool used by machinists called a “ball gauge” which is used to measure the diameter of holes. The tool is inserted into the hole, or chamber, opened by turning the control screw, removed and the outside diameter is measured with a micrometer. There are also ball micrometers available for purposes like this. Has anyone ever thought of trying this to get a definitive answer on the supposed difference in chamber size between 5.56 and .223?

  33. The 5.56 military SS109 round does fire at higher pressure than the civy .223 round. The opposite is true with the 762×51 military round. The .308 has more juice.

  34. I keep hearing talk about the differences in chamber size between .223 and 5.56. If anyone has any official documentation showing these differences I would like to see it. I could be convinced that military ammo is manufactured to higher pressure than civilian ammo(I could be convinced. I’m not yet.), but I don’t believe there is any difference in chamber size. If the 5.56 was even a few thousands larger then the .223 it would not chamber in a .223 and allow the action to close. Also the .223 might chamber in the 5.56 but the headspace would be to much and cause dangerous gas blow by. I have checked three different reference manuals and they gave the cartridge or chamber dimensions for the “.223/5.56nato” round. Right now I want to repeat something I said in an earlier post to this blog. If you have ammo that has 5.56 on it, it is not military ammo. At least not made in the USA. Ammo made in the USA for our troops does not have the caliber stamped on it. It has the armory where it was manufactured and the year. For instance ammo manufactured in 1977 at the Lake City armory is stamped LC 77. It doesn’t come in fancy cardboard boxes either. It comes in bandoliers packaged in ammo cans. Anything else is just paramilitary marketing. This is one of those issues that has been told as truth for so long that everyone assumes it has to be true. Even a host on a shooting TV show mentioned it. When the guest for the show questioned him on it, the host said it was common knowledge. When the guest wanted proof, the host said he would get and edit it in at the end of the show. The show ended with credits which were followed by the disclaimer “It is up to each individual to determine what ammunition is safe for their firearm”, I’m sure if the host could have proven the differences between .223 and 5.56 it would have been in the show. Not the disclaimer, which by the way has not been on any other episode I have seen. One final not on pressures. Higher pressures, while creating higher velocities also create potential problems. Higher pressures cause the brass to expand faster and more firmly against the chamber wall. This requires more force to extract and a stronger extractor. Military ammo is manufactured for semi, or fully automatic weapons that have to function every time without fail. Every failure has the potential to represent a dead soldier. While the AR is becoming more and more popular in recent years, the commercially available .223 has been predominantly a varmint cartridge fired in strong reliable bolt action firearms. You decide which is more likely to be manufactured with higher pressures. Thanks for taking the time to read this post. For more detailed information on this subject look up my previous post early in this blog. Gary

    1. The dimensional specifications of 5.56 NATO and .223 commercial brass cases are identical. The cases tend to have similar case capacity when measured, with variations chiefly due to brand, not 5.56 vs .223 designation. The result of this is that there is no such thing as “5.56 brass” or “.223 brass”, the differences in the cartridges lie in pressure ratings and in chamber leade length, not in the shape or thickness of the brass. The 5.56 chamber allows the 5.56 (hotter load) to be fired safely creating about the same pressure found when firing a .223 round in a .223 chamber.

      It is that simple and nothing else needs to be said other than it is not completely safe to use 5.56 ammo in a weapon designed for .223 only.

  35. Now add the the confusion the .223 wylde barrel that splits the difference of .223 and 5.56 nato chamber.

  36. Thanks for this article. I have been asking the 5.56/.223 question from many people (even sporting goods stores) and have not received a good answer. This article clarifies the what and why! Good job and good shooting.

  37. If the barrel has .223 stamped on it, then you can NOT fire the 5.56. If it has 5.56 stamped on it, then you CAN use both rounds safely. Having both weapons is fine, especially if the twist rates are different, which allows you to fire 52 grain up to 77 grain. I hope that’s the case with your weapons.

  38. how can I find where to get the best price for an ar-15? there’s so many these days. you always here from someone saying, I wouldn’t have paid that price, you should have checked out so and so. fixing to buy my first ar-15. in 5.56 of course. but how can I find the best price for one? if there is such a way. thanks for any comments on this.

  39. Are we all in agreement that it’s OK to run both .223 & 5.56 through a Mini-14? I’ve heard from many different people that yes it’s allright except for the newer ones 2006 and up and I’d like to know for sure from all reliable sources. Mine’s a 1991 and I’ve owned it for a couple of years, really haven’t shot it much but it’s sure a neat little rifle. And I sure don’t want to do any damage to it.

    1. JD, I’ve never owned or fired a Mini 14. They are built on something closer to the M-14 action than an AR action. The M-14 is a strong action and everything Ruger makes is well made. Personally I don’t believe it would be any problem, but give Ruger a call. 603-865-2442 They won’t BS you.

  40. What about the 4th type of chambers the “WYLDE”, I have couple of RRA AR’S with a WYLDE chamber. That is one of the reasons I went with RRA because it can safely shoot both .223 & 5.56 rounds. I even talked to RRA before buying them asking this specific question. Between the 2 RRA’s I have shot a few thousand rounds & only had a few get hung up on ejecting, none that I can remember when ejecting a live round. Even though I’ve never had a problem was I lied to by the people at RRA about the gun being able to safely shoot both types of ammo?

  41. I reload 223 and 5.56 brass for my Mini-14. What is your opinion regarding the safety of reloading 5.56 brass to 223 ballistics and using it in a rifle chambered for 223?

    1. I started to answer this with a quick statement, rather than go on and on like did in my previous statement. But as I started to answer it in my head I kept saying that needs a little explaining. Then that needs a little explaining, and so on. So I will try to answer the question first, then I’ll elaborate. I will however try to keep it short this time. As long as you are not working with maximum loads the 5.56 brass can be reloaded to .223 “ballistics” and fired safely in either rifle. I must immediately explain though that “ballistics” is what the bullet does after it leaves the barrel. The velocity and trajectory can be duplicated with either cartridge but you have to manipulate the load data to do it. The rest of what I am about to say is comparing commercial .223 brass with military surplus brass. Not all brass marked 5.56 is military surplus. Some of it is plain old .223 brass marked 5.56 to market it to the paramilitary types. If you are not sure treat it as if it is military surplus. If your brass doesn’t have .223 or 5.56 on the head stamp, and you are sure that is the caliber, you can be sure it is military surplus. Most ammo manufactured in the US for the US military is head stamped with the initials of the armory where it is manufactured and the two digit year it was manufactured. For example brass head stamped LC 72 was manufactured in the Lake City arsenal in 1972. That being said, why does it matter to a reloader. The .223 and the 5.56 have the same outside dimensions. Since the brass is thicker on military surplus cases there is less case capacity inside. If you use the same amount of powder in a military case you will have higher pressures. If you were loading the .223 near maximum pressures as indicated in a reputable reloading manual, using that same amount of powder in military brass is very dangerous. Most experts and manuals recommend backing down from there posted loads when using military surplus brass. 10%for moderate loads and 15% or more for maximum loads. Then, if that load shows no signs of excessive pressure when fired, you can add 1 or 2 grains of powder and try again. Continue this process until the fired brass shows signs of excessive pressure or you have reached a load you are happy with. If the brass shows signs of excessive pressure back off on the amount powder to the last load that didn’t. If you are not prepared to do this testing when reloading then don’t reload military brass. I hate to sound like a disclaimer but I have to say anytime you are working at or near maximum pressure loads, you are doing so at your own risk. If you make a mistake, you will be the one paying the price. Keep in mind also that some powders are sensitive to temperature changes. A load near maximum pressure that is safe on a twenty degree day in January, may not be safe on a ninety degree day in August. Let us not forget the primers. Not all small rifle primers are the same. The pressures they create can change slightly from one manufacture to another. That change is exaggerated at higher pressures. If you create a load that is near maximum pressure, then change primers, ie. Remington to CCI, CCI to Winchester, etc., you need to back off an the load and work your way up again. By now I bet I have scared off several potential reloaders. Please come back. Reloading is a very safe and effective and fun way to create ammo. If you get a reloading manual produced by a powder or bullet manufacturer and keep your loads in the midrange of the data provided you will create safe ammo the is faster and more accurate then most factory ammo. Then after you gain experience if you want to play with your loads to make them faster, or tighten up the groups even more, or reduce the loads way down to train a recoil sensitive shooter, you can do that safely too. But there techniques and processes you have to follow to keep it safe.

    2. Hi still have a ? I have an ar with a bull 223 barrel and still dont
      no if its safe to shot 5.56 threw it , I dont no why I got the 223 barrel
      because my other ar is a 5.56. and dont want to mix up the ammo.
      I really dont see any problems but never no, if you could get back
      cause really dont want to buy another barrel. thanks for time and
      getting back. ( its not that I dont understand I have MS and my mind
      sometimes miss understands) thanks again for reply..

  42. Please tell me you’ll actually read articles before printing something this ill informed in the future. The only difference in the two is that 5.56×45 and .223 are manufactured under different standards that set different pressure level limits.

  43. I admire this man for his service to our country, but after reading this article I’m sorry but I can’t call him a firearms expert. What gives me the right to say that? Nothing really. I am a shooter like most of the others here. Have been for over 50 years. I have been a reloader for over 40 years. I’ve been a firearms safety instructor for nearly 35 years. I was a gunsmith for 22 years. Now for the article. Mil-spec chambers are slightly larger than civilian chambers. Very slightly. The difference is measured in 10’s of 1000’s(.0001). They also have a longer free bore (the distance from the case mouth to where the rifling starts). It’s not so it can handle more pressure. It’s so during combat the weapon will feed reliably in filthy conditions, with ammo that is dirty, or corroded, or other wise mishandled. Military rifles just have to go bang every time. They don’t have to hit a quarter at 300 yards. Sniper rifles excluded. That dirt, dust, mud, water, or even oil can really mess up things, But the rifle still goes bang. Mil-spec ammo is not loaded to higher pressures than civilian. In fact some manufactures have at least one line of ammo loaded to pressures much higher than military ammo. The only real difference between military ammo and civilian ammo is the brass. Since the dawn of firearms, successful military calibers have been taken up for civilian use. Modern brass cartridges are no different. Whether it was the .45 ACP in 1911, the M-2 aka .30-06 Springfield, 7.62 NATO aka .308 Winchester, or 5.56 NATO aka .223 Rem., the only difference between military and civilian ammo is the gauge or thickness of the brass. Military ammo has thicker brass walls so it is less likely to be damaged if or more likely when it is mishandled. Since the outside dimensions of the cartridge are unchanged, the inside capacity is less. The manufactures know this and they use the proper type and amount of powder to produce safe pressures. Reloaders using loading data developed with civilian brass have to be aware of the reduced capacity in military brass, but this is not an article on reloading so that’s enough said there. How much free bore a chamber has varies by manufacturer and has nothing to do with civilian versus military, except for reasons mentioned earlier. I do agree however that military ammo is not burdened by SAMMI specs for overall cartridge length. If you use ammo that you haven’t verified cycles through your rifle without problems you may have a mess on your hands. Or worse! The one thing that really forced me to comment on this was the idea of rechambering the .223 to the 5.56 specs. First he tells us that the 5.56 has higher pressures than the .223 and can damage the upper which has nothing to do with the chamber size, but then he tells us we can remove more metal from the chamber to make it safe. In fact it can be done safely but the logic doesn’t follow with the rest of his argument. By the way I said it could be done safe. I didn’t say it was smart. Anyone with an $80 reamer and a $30 handle and a $30 headspace gauge can take out the extra metal. However the next time you go to the range you will kick yourself in the @$$ for it. You will have screwed up the barrel. It takes a qualified gunsmith with experience in chambering to cut a new chamber and keep it true to the original bore. I’ve already told what his tools cost. Double that for his experience and you will realize it will be cheaper to just buy a new barrel with the chamber you want. You can swap out the barrel yourself with about $40 worth of tools and you really need those tools to properly clean and maintain your AR anyway.

  44. As stated in the article, most of the .223 and 5.56 barrels have chrome lined chambers & bores.
    If you ream the .223 chamber & throat to 5.56 specifications you will remove the chrome.
    I suspect that that would not be a good thing.

  45. Could we finally at least get a comment FROM SOMEONE WHO HAS ACTUALLY HAD A PROBLEM with an AR and the ‘wrong’ ammo?
    Im reading ‘expert opinions’ and other stuff for years now but no one has said, “HEY I HAD A PROBLEM BECAUSE….
    Thank you.

  46. I had a very knowledgeable person explain this exact situation to me years ago. When I went to buy my AR, the counter person tried to tell me there was no difference. I stuck to my guns and asked to see the info on the weapon and it was a 223 not 556. I even checked the stamping on the barrel and it said 223. I left and went to several outlets and finally found someone with the sense to understand weapons and I finally purchased my 556. Great article

  47. Yes, it Is agreeable to fire a .223 in a 5.56 chamber, but when it comes to reloading you must be extra careful on resizing your .223 brass. If you don’t set your dyes right and inspect the case’s shoulder measurements and length, you could find yourself stretching the brass of the .223 too far when fired, because of the 5.56 chamber being slightly larger. The case will want to expand to that size of the Chamber and if it gets stretched too far you might end up splitting the case. Also keep in mind that .223 casings are thinner than a 5.56 case, making the .223 case expand easier and more prone to splitting. So check your measurements when reloading and be safe. Just remember this isn’t an issue when you have new .223 ammo, only if it’s used and you are planning to reload it.

  48. Pingback: Top 10 AR-15 Posts
  49. I still cannot figure out why anyone would manufacture a .223. Or why anyone would buy a .223.
    Is it just me or am I confused. My Armalite is stamped 5;56.

    1. For an Combat AR I see what you mean, but for a precision AR you would probably want .223 rem. Most precision ARs are .223 wylde which is in between .223rem and 5.56 spec wise and can use both cartridges.

      Also, 98% of bolt actions are .223 because there aren’t too many 5.56 hunting rounds. The only 5.56 bolt action I can think of right now is the Mossberg MVP which accepts AR magazines too.

  50. Just now saw the thread from Dan. Is all commercial .308 Winchester 58,00 PSI? Guess I’ll be selling some .308. Thanks again guys, you might have just saved a very nice M1A and possibly it’s owner.

  51. It does indeed help. Good to know because I’ve been using both on the Mini-14 going by what I’ve heard and read. Now I just bought 500 rds of 7.62×51 for the M1A and was sweating that a little, glad to hear it’s OK from someone who does seem to know what the’re talking about in technical detail. You know when I bought the M1A (built in 2010) I picked up some American Eagle .308 cause that’s what the Springfield manual said to use (along with the 7.62) and have run maybe 100 rounds through it. Hope everythings OK, believe I’ll check somewhere and find what the pressure is on that ammo. Hey thanks immensely for all the feedback and info, I really like my firearms and want to take good care of them. And not feed them ammo that’s a little too strong or ever so slightly the wrong size. All good stuff to know.

    1. I’ve been staying out of this .308 military vs civilian discussion because the original discussion is about 223 vs 5.56 and the author wrote he would follow up on the 30 caliber debate.
      But………google “7.62×51 vs .308” and read the thread on “the high road dot org”. Read the entire thread.
      As i said on the 223 vs 5.56,the only way to be sure is to perform a chamber cast. If you don’t think you can,find a known good gunsmith who has done a chamber cast.
      You may also want to google “psi vs cup” and note that time is a critical component.

  52. Exactly right!!! You can use the 762.51 in a .308 but you can’t use .308 in a barrel stamped for 762.51. Reason being the .308 is a higher pressure round, I’m thinking about 8,000 more PSI than the 762.51. I believe the .308 is rated at 60,000 PSI and the 762.51 is rated at 52,000. I shoot both in my Rem 700 AAC TAC .308 barrel and can actually feel the .308 kick a tad harder than the 762.51. Happy shooting folks.

    1. Oops! Here we go with the weird “pressures” ideology. FYI, I have two made in Germany H&K rifles, one is 5.56 NATO and the other 7.62 NATO. The outside diameter of both barrels and chambers in identical. The 7.62 NATO is just a 5.56 NATO barrel that is bored out to the larger diameter 7.62 NATO. Therefore the chamber and bore thickness is thinner on the larger 7.62 NATO barrel. H&K has never published any literature advising against using commercial .308 Win. ammunition. Sorry.

    2. Some of the information on the differences between the .308 Winchester and the 7.62×51 Nato which I have seen put forward here is correct, and some of it is not. If you look at the diagrams of the two cartridges as set out by the US ordinance department and by SAAMI you will find that they are identical externally. As to pressure ratings, the original test cartridges were rated for higher pressures in the Nato round but the pressures were dropped to a lower requirement after Winchester adopted it as the .308 in 1952. MAP for the 7.62 is an average of 58,000 psi, while the .308 is 62,000psi. This is a difference of only 4,000psi. Also, the Nato casing has a thicker case webb and body. It has to have this because it is fired in machine guns, which fire from open bolts, and are ejecting the casing while pressures are considerably greater than something like an AR10 or an HK 91, an M1A or an FN FAL, all of which fire from closed bolts, and have lower cycling rates/times, allowing pressure to drop more before unlocking and cycling the action. The lower pressure and thicker casing allows the cartridge to be more reliable in machine guns, which is what it is mainly used in.
      As I look at the latest Hogdgen Annual Reloading Manual, I see a list of maximum load pressures ranging from 55,000 psi to 60,000 psi, most of which would be within the Nato specs. The real difference between the rounds is the chamber dimensions of the standard .308 and the military 7.62 Nato. The Nato chambering is deliberately made slightly larger and longer than a standard .308 Win chamber. This is so that the rifle or Machine gun can use 7.62 X 51 ammunition made by, say, Spain or Greece, or maybe France, which is not made to perfect specifications. All of these weapons will pass a check with a field gauge, which means that their headspace is still within safe parameters. If the chamber has sufficient slop, such as some of the Mausers which have been converted by Spain and some of the BM59’s and 62s, firing the thinner walled .308 Winchester rounds in them can result in case head separation. However, the M1A from Springfield and the Fulton Armory M1A, the AR10’s being manufactured here in the US, the HK91, and several other 7.62X51 semi-auto rifles such as the FN have chambers which are at least as tight as a Remington 700 or a Ruger in .308. In the case of the M1A, the chamber is reamed to match grade dimensions. It is designed to shoot both rounds from the ground up. A number of these manufacturers even base their accuracy guarantee on the use of either Hornaday, Nosler or Federal match .308 Winchester ammunition. I’m pretty sure they wouldn’t recommend these match loads in .308 Winchester if it would hurt either the rifle or the shooter. They will, however, tell you not to use .308 light magnum or Superformance in their rifles, due to the higher pressures at the gas port, which causes the piston to move the operating rod too fast, which can batter the bolt or bend the rod. But if you’re worried about this, email Springfield Armory and ask them. They made the rifle and they will know more about what you can feed it than any of us internet rangers. Oh, and they will be correct. They made the rifle. They tested the rifle. They chambered the rifle. They will know what it will shoot safely.

  53. As far as the Mini-14, you can safely use both .223 & 5.56 NATO.The Mini-14 non-target versions can fire both the .223 Remington cartridge and the similar military 5.56x45mm cartridge. The target model Mini-14 rifles are chambered only for the .223 Remington cartridge. If in doubt, contact Ruger and they’ll be able to tell you, usually based on the serial #.

    So 7.62mm ammo fits nicely into .308 chambers, as a rule.” You CAN encounter problems going the other way, however. A commercial .308 Win round can exceed the max rated pressure for the 7.62×51. So, you should avoid putting full-power .308 Win rounds into military surplus rifles that have been designed for 50,000 psi max

    Hope this helps!

  54. Well I don’t own an AR-yet. However I do own a Mini-14 and an M1A. And as I said a lot of guys say these rifles can use both types of ammo, the Mini .223 and 5.56 NATO and the M1A .308 and 7.62 NATO. And I own both kinds but you know I can always sell what I shouldn’t use. So tell me, can these particular rifles use both types of ammo? Don’t want to take a chance on a serious problem.

  55. The article writer has muddied the water more than he’s shed light on the situation. There is one difference and one difference only between .223 Remington and 5.56 NATO chambers. It’s the throat or leade area (same thing). A 5.56 chamber is made to shoot heavier bullets with stronger powder charges, hence the longer throat and more gentle angle of the rifling. The .223 chamber is made to give the best accuracy possible with 40-50 grain bullets, which means being shorter, necessitating slightly lighter powder charges. It’s exactly the same thing that Weatherby does with their chambers. A 5.56 chamber or a Wylde chamber (which is a compromise) will shoot either ammunition safely.

  56. Dammit this shouldn’t be an issue. Either there’s a big difference so there’s no argument or there’s no difference so there’s no argument. This is potentially a dangerous situation and ammo manufactures should be held liable. OK how about a Ruger Mini-14, 99% of what I’ve read says both 5.56 NATO and .223 is safe or a Springfield M1A using .308 and 7.62 NATO? Bottom line, is what’s stamped on the receiver what the rifle chambered in, no argument?

    1. The correct caliber for the AR-15 platform is stamped on the barrel, and not on the receiver. You may find 5.56 stamped on the receiver, with a 6.8 SPC barrel on the upper… etc.

      Looks like this thread is going to be here ad infinitum…

  57. I knew my Southern Scotish Brother would put my mind on the right track. I am Scot/Irish from the Webster/Wallace Clan and I appreciate you pulling me from the mire my friend. The 193 was the round I was trying to pull out from this cobweb enclosed dungeon of lost brain cells, much appreciated Sir and cheers back to my Scotland home.

  58. Hi Dan. The round you may be thinking of is the M193. This round was developed to impact at a high velocity becoming unstable upon impact potentially creating a greater permanent wound cavity and dispatching your adversary. My references are as follows; Dr. Martin Fackler, F T Chamberlin, Gun Shot Wounds, in Handbook for Shooters and Reloaders, Vol. II, Ackley PO, ed., Plaza Publishing, Salt Lake City, Utah, 1966; B Sturtevant, Shock Wave Effects in Biomechanics, Sadhana, 23: 579–596, 1998; and American Rifle: A Biography, Alexander Rose (2009) p. 375-376. From one Southerner (southern Scotland) to another Southern Gentleman. Cheers

  59. Look it up and do a little research on the round. The 5.56 tumbles after entering the body. That’s one of the reason it’s wounds are so nasty. It’s a know fact, however, they don’t tumble in flight, that’s B.S.

  60. Sometime between leaving Nam in 1970 and retiring in 1994 I heard, read or whichever (can’t recall) that Rem were making the .223 to tumble after hitting soft targets but damned if I could tell, damn bullet goes so fast I couldn’t even see it leave the barrel. Now I was just repeating what I heard that’s why I didn’t apply a reference and I’m real sorry if I got you riled up and all but I’m just a stupid old boy from the South and probably ain’t as smart as some but I’m just a Rebel by choice, Southern by the Grace of God. And, your parents should have tought you to be kind to strangers and old folk.

  61. Agree with getting hit with the .223. This round is supposed to tumble when hitting a soft target, and the penetration depth is anywhere from 10-13 inches in gel, the 5.56-109 (which I prefer) will exit through the bone and body cavity, but will also disable smallish military vehicles. My ARs are A2s pre Clinton ban and are “real Colts”, one drawback the trigger pins are .250 versus the .176? pins used in newer ARs and I have had a hard time finding dropin triggers……unless I change to a newer lower which would hurt the value of my Colts. Had a lengthily convert with an anti-black weapon guy and finally told him to shoot me with a .223 or 5.56 but don’t shoot me with a .762/.308 or larger cal hunting rifle because he said hunting guns were ok but the black ugly gun was the worse thing on earth???? He did not comment back…..

    1. “This round is supposed to tumble when hitting a soft target,” Horse crap. Show me a design spec for that one. Just because the projectile might yaw after impact, does mean it was designed to do that. There have even been “reports” by ignorant fools that the projectile is designed to tumble during flight. Again, horse crap.

    2. RD……the moderators didn’t okay my posting a link for you to read.
      But if you google “small arms calibre debate thinkdefence uk” you may find the article. Note the reference to the M193 Vietnam bullet.
      Not sure of your age or your combat experience but this fills in some of the gaps of my replies to other comments on this topic.

    3. Geissele makes drop in triggers that use the larger pins that are used in the old Colts. Also, they are some of the best triggers on the market

    4. Well I thank you a bunch Jon, hell I got cussed out something terrible just by saying a .223 tumbles on another post. And you are right bigtime, they sure are good triggers. I thank you again Jon and will hunt one down on the Internet for my 5.56. Appreciate it a bunch my friend.

  62. JR……no one round or bullet will work in every battlefield… least for the platform we are joined at the hip with.
    What worked in VN (and some say the 5.56 rounds didn’t work effectively) may not perform in all conditions in another conflict. Afghanistan and Iraq are prime examples. From house to house fighting to across wide mountainous terrain…..either eyeball to eyeball or across a valley.
    That is why the Marines and the Army started toying with different bullet weights for their distinct battle weapons. New cartridges (6.8) were engineered and old ones (7.62 short and long) dusted off. The M14 enjoyed a new resurgence tho limited. 50 cals came to the dance in new attire.
    Don’t forget……if you don’t out-right kill the bad guy at least wounding him puts him out of action for awhile. Put more rounds into his hide and he’ll be on the mend longer……if he can get medical treatment at all……infections can kill.
    Every weapons platform has had its supporters and opponents.

  63. My opinion and I tested into BODY ARMOR with both even SS-109s —if you want very light weight HIGH SPEED round go with 5.56 but it is not a MAN KILLER meaning I shot the .223 HP 62 grain into Gelatin and I must tell you I would not wan tot get hit by that at 100 ft. the 5.56 is much faster and does not have the lethality of a good Silver Bear HP nickel plated round…even the SS-109 is BS it will pass right through a human target bone and all and that person will live to fight another day and I believe the .223 is much more devestating a round fired from an M-4 COLT?

    1. “if you want very light weight HIGH SPEED round go with 5.56 but it is not a MAN KILLER”

      Hmmmm, I have to wonder what these little Winchester 40 Grain Frangible rounds would do to a ‘bad guy’. I have to think that having a 40 grain high speed .223 round disintegrate/explode through your chest cavity would put you out of action pretty quick. Yeah, that would violate the Geneva Convention, but then again…I’m not a military combatant.

  64. Yep, the Wylde chamber is the only way to go if you have a .223 and want to throw some 5.56 downrange. I only purchase 5.56 type weapons if I want to fire .223 ammo also. Now, why not get on the .308/762.51 bandwagon. I have been told NOT to shoot 762 in a .308 chamber and I told the guy they are the exact same thing……….any comments on that?

  65. old dorgunr! Well i guess i felt it was a can of worms that needed to be opened on a post like this….great info and thank you for adding the specs here i am sure they will help out. there seems to be quite a bit of misinformation and lack of education when it comes to the .223 Wylde barrels…well barrel chambers in general…and you make a great point that people should pay attention to when talking about chambers…their are lots of manufactures out there and not all of them use the same reamers and some even make their own reamers…so there is always some minor differences in chambers from one manufacturer to another…and i agree 100% with advocating a chamber cast….again thank you for adding the comment …very useful visual effect

  66. i would like to clarify the confusion with barrels marked 223/556..these barrels are known as .223 wylde….not going in to specs but it is a hybrid between the .223 match and 5.56 chambers….they are used a lot by comp shooters.. they were designed to shoot .223 rem and 5.56 mil-spec/nato ammunition safely…basically they have the slightly larger 5.56 chamber and throat with the tighter bore/barrel of a .223 match…they are made this way to get the accuracy of shooting with a .223 match barrel while being able to safely shoot both .223 and 5.56 ammo…i hope this helps someone out there…if you still have any question i suggest you look up the 223 wylde chambered barrels…they are great barrels for people looking to get the most out of their rifle with both types of ammo

    1. Now you went and opened the big can of worms! 🙂
      Just to add to your post……i’ll throw in some common/popular chamber measurements…..a visual effect in words.
      The SAAMI chamber specs for a 223 Rem is around 2.410″.
      A Derrick Martin chamber is 2.442″
      A Wylde chamber is 2.445″.
      A AMU (Army Marksman Unit) chamber is 2.500″
      The NATO chamber is around 2.550″

      The middle three chambers are designed around primarily the Sierra Matchking 80 grain bullet used in competitive long range shooting.
      Shorter (lighter) bullets work well in them without having to experience that “leap of faith” in a NATO chamber.
      The SAAMI 223 Rem chamber spec was standardized a long time ago for bolt action rifles. Way before the AR-15 craze commenced.

      Clear as Rio Grande mud,eh?

      That’s why i advocate a chamber cast. Lots of manufacturers with lots of chamber reamers.

  67. Can someone confirm that the “match” chamber that is briefly mentioned is the same as a “Wylde” chamber? Also missing is any discussion about running 5.56 through a Wylde chamber…Is it really ok and does it really increase accuracy on the 5.56 as well as the .223?

  68. If you really want to make sure…….buy some cerrosafe,learn how to use it (youtube or goggle it),remove your barrel and make a chamber cast including the leade/throat.
    Just remember cerrosafe readings can vary with time and temp.

  69. Some of us simply bought one each, never knowing the availability of cartridge caliber in the future. If they interchange, fine, if not, fine. You are covered either way,
    As far as the ‘heavy bullets’ are concerned, my money is on the Russian AK in the 5.56 x 45 NATO caliber. Great design, reliability. Not nearly as powerful as the original caliber but neither is the .223 anyhow. The AK design utilizing the 5.56 x 45 is ideal for the pistol length AK. Its really manageable even for women. Back to it all depends on what you are looking for and what your end use will be.

  70. Trust the manufacturer. Don’t trust anyone else!

    The manufacturer doesn’t come by this information in a vacuum, and he doesn’t rely on information blogs like this one to get his knowledge. He IS the knowledge. He’s the source of all knowledge concerning his guns.

    Two things must occur in order before a manufacturer cuts a chamber, and they must be a coordinated enterprise.

    (a) He must decide what specification reamer he will use, and will stick to that for every gun in that series, in a well-intentioned hope that gun buyers aren’t confused about what HE recommends, as is the case herein. He might even make his own reamer, machining it according to SAAMI or NATO specifications. They are distinctly different, and he’s NOT clueless about the difference, and doesn’t need to refer to one of the experts on this blog.

    (b) He must “proof test” his gun before one of his testers wields a mighty hammer onto a stamped proof mark when the gun holds together under an INDUSTRY APPROVED PROOF LOAD that is available ONLY to gun manufacturers BY ammo makers (Federal, Winchester, Remington, etc.).

    The manufacturer (not a gun builder of parts made BY gun manufacturers), KNOWS the dimensions of his chamber reamer, and he KNOWS what proof specifications were purchased when he bought proof testing ammunition, whether it was SAAMI or NATO specification proof testing ammunition.

    Proof testing has been going on for centuries, since the advent of gun powder and the earliest guns, so that some King’s soldier didn’t have to worry whether a gun would fail under his chinny-chin-chin and loose the King’s battle.

    Rather than speculate about what a gun is built and tested to do, one simply confers with the maker of the fine barrel. And, if it’s not a proof tested barrel, it’s not a gun barrel. It’s a pipe that some fool might play with, but it’s not a gun barrel.

    Please don’t confuse gun “experts” with gun makers. Gun experts examine what’s inside a gun. Gun makers know, because they put it there. 😉

    1. I know this isn’t “politically Correct”….but I am new to all this. When the whole Sandy Hook anti-2nd Amendment thing happened we started to excercise our Second amendment rights.

      Long story short I have a Bushmeaster that is stamped .223-5.56 MM

      With this info can I infer that it IS chambered for 5.56.

      Likewise I have a mini-14 that is stamped .223…… I called Ruger before I bought it and gave the serial number etc…. they told me it would shoot any 5.56.

    2. I agree with you. This gun expert needs to look up who designed the 5.56 x 45 and who came out with the 223. Okay I’ve spilt it already it’s Remington. They are the same. I want to know how you blow out primers. Do they come through the bolt?

    3. The excess pressure enlarges the primer pocket enough that when the case is ejected, the primer stays put, then falls off the now-empty bolt-face and drops into the action. Also the reason that 5.56mm ammunition has crimped primer pockets (to further prevent this potential problem).

  71. if you cant clearly get the picture with the stamped numbers on your weap. and this suitable explaination, you shouldnt have a gun!. yes, we are losing our rights, ei; the increase in prices for everhing. our governments stealing private funds by any and every means; our spineless elected officials immunity from prosecution for criminal activities contrarary to our contitution, is ” trespass of treason to the constitution. point them out, vote them out and hold them accountabe!

  72. So you let some geek act like an expert on here. How many rounds has he put through each chamber? What research into the SAAMI concept has he done. A well made rifle will fire either round without incident. The most plentiful ammo is military surplus and works fine through all the commercial 223’s I have built. Your real issue lies when you get into custom built rifles some of the chambers for accuracy are made a bit tight. When this happens military and even cheaper ammo may not function well. Military ammo is not on the weak end of the scale but you can buy hotter commercial 223 than what the service uses. I despise guys like this talking out their ass

  73. I own a Smith & Wesson M&P 15 that states you can shoot 556 or 223. You are telliing me I do not need to shoot 556 ammo in this gun?

    1. Your question contained the answer! The MANUFACTURER stated that you can use either. THAT’s the answer. I speak as a factory trained and certified police armorer for S&W, Ruger, and Remington, and the same goes for all guns made by any company. THEY are the absolute and ultimate authority, and nobody else.Smith & Wesson knows their gun better than any armchair expert. Either ammo is perfectly good. .223 Rem can ALWAYS be fired in a 5.56 NATO chamber, but 5.56mm can ONLY be fired in a chamber that is so classified by the MANUFACTURER as such, built with a specially reamed 5.56mm leade and pressure TESTED to the higher pressure limits. If S&W, Ruger, or any other company has made that specific distinction, you are always good to go. If the MANUFACTURER did not state that it is a 5.56mm spec chamber and 5.56mm spec pressure test, then it is categorically NOT. Gun magazine article writers, gun shop owners, blog editors, hobby gunsmiths, and other freelance agents of coffee cup “wisdom” have no authority to pontificate, or otherwise speak for the manufacturer, who designed, tested, and built your gun. Look to your owners manual, and only your owners manual. They are all you need. That goes for all guns, in any caliber. By the way, “putting parts together” and assembling a gun from manufactured specification parts does not make one a gun manufacturer. AR-15 uppers are made to one specification or another, chambered and pressure tested for one specification or the other. If I buy a 5.56mm upper, then my AR becomes a 5.56mm rifle, that can always handle the lesser specification. If I buy a .223 Rem. spec. upper and substitute it on the same gun lower assembly, it becomes a .223 Rem. gun, that has insufficient chamber dimensions to safely shoot 5.56mm ammo. To shoot higher pressure 5.56mm ammo in it is something you should leave (at a very safe distance), to purveyors of some other “wisdom”. Period. I mean, PERIOD.

    2. Thanks for asking that question of that gun, I have been looking to purchase a Smith & Wesson M&P Sport


  75. where does that leave .223 wylde? i hear its reliable, safe and accurate with both types of ammo. does it live up to the hype?

  76. What about the .223 Wylde chamber? It is supposed to be a compromise between the true .223 and 5.56 chambers that will allow you to use either round but still maintain some accuracy when shooting .223.

    1. That’s what their manual states! Ruger is a GUN maker that adheres to the reality that only they are responsible for the safety of their guns and the specifications. Nobody knows their product better than they do.

      WHY would you go elsewhere for a recommendation about the specifications of their product?

      To answer your question; YES. Emphatically yes. Most assuredly, yes.

      Do you really think for an instant that they don’t know about the engineering and specification of their own product, and that they are just making false claims about something that can be measured in a court room against a blue print after someone sues them? Oh, my.

  77. Ned Christensen of MichiGuns, makes and sells 223/5.56 gauges to check the chamber in your rifle. He also makes a 5.56 reamer that works very well to convert your 223 to 5.56.

  78. H&K’s MR556A1 is chambered mil-spec 5.56, but the bore is not chrome plated like it’s military cousin, the M-416. The reason is that H&K feel that the chrome lining can mask imperfections, thus affecting accuracy. The M-416 is chromed because that’s what the military wanted.

    1. Sorry, but any such claim is entirely fictitious, advertising bunk. I was a precision electroplater for a number of years. Plating does NOT mask imperfections. It is not a chocolate dipping process. Plating is extremely thin, on the order of .0002″ thick (two-ten-thousandths or more–not much more), and is actually electrically attracted to HIGHER surfaces and edges, thus it would make any imperfections more pronounced, building them up.

      Engineers had to factor that in when designing threaded components for the co-ax connectors and other precision parts that we made for the aerospace and telecommunications industry . They had to allow for enhanced building of raised surfaces.

      Secondly, electroplating is attracted to the surfaces of the part–called the cathode–, which is CLOSEST to the anodes in the plating tank, and the electrons flow past hidden surfaces and deep hollows. If you simply immersed a gun barrel with its small opening into a plating tank, with the outer side masked with industrial platers mask (something like the rubber on your pliers), the interior of the barrel would be plated to the first inch or so, and thinly at that, tapering to nothing inside. Electrons flow directly from anode to cathode, and reflect to a degree, but don’t follow contours.

      In order to uniformly plate the inside of a part, whether it be a co-ax connector, or a long thin rifle barrel, the electroplater must devise extremely sophisticated and exacting procedures to (a) mask the outer parts of the barrel to avoid plating, (b) stretch an anode wire down the exact middle of the barrel, so that the plating is the same thickness on the entire interior circumference. This is NOT a money saving process that is used to “mask” imperfections! It’s labor intensive, and very costly. The US Military does it because they have access to your generous Tax-Dollar contribution; not because they are pandering to a sloppy gun maker. AND, what’s more, if the plating isn’t done with exceptional professionalism, it will not adhere under the stress of firing, and will immediately begin to peel at the junction of bare metal, most particularly at chamber and crown, like a cheap screwdriver does.

      Please understand that chromium is the alloy that hardens steel — i.e. “chrome-moly”. Higher percentages makes it more corrosion resistant, thus, being stainless of one grade or another. Industry plated HARD CHROME, applied by galvanic action (anode to cathode), lays down a microscopic layer of protection that gives the interior of a barrel exceptional slipperiness, resistance to premature erosion at the leade (tapered rifling immediately in front of the chamber). The military WANTED their guns chrome lined because they are harder, and last longer. It has no effect whatsoever on accuracy, except for the better. H&K’s advertizing department cannot alter physics.

      Plating is NOT applied to a barrel to mask imperfections. Any imperfections that are there or are not there cannot be altered by plating. H&K is a very good rifle maker, but beware of nonsensical claims.

  79. yas all are over reacting too much on these issues. safety is always the most important concern! I’ve been building baby black rifles over 3 + decades,if it’s a quality built rifle,223 or 556 makes ( NO ) diferance what You feed it,if it’s maintained properly,it will give You a life time of enjoyable accurate problem free shooting. Also the same goes to Your 10mm-40cal. issue. As long as it’s a quality made firearm;colt,ruger,or smith etc. , You can safely shoot 40’s all day long thru Your 10mm. mag. All a 40 cal. is only an 10mm. mag ( short ). Don’t be a bunch of worry warts, go put in so fun quality range time in with family & friends 🙂 no go

    1. Comments like you just made concerning .40S&W/10mm are idiotic and will likely get someone injured who does this on a regular basis, or at the very least damage their pistol. Do you know why? Probably not!

      As I already said above, both cartridges head space on the case mouth. In older Glocks chambered in .40 S&W there were a LOT of case failures The reason is because there was too little support of the case while in the chamber. That was solved by reconfiguring the chambers on replacement barrels. Now you want to recommend to people that they create the same sort of condition in a 10mm pistol by firing the shorter .49 S&W round in it and telling people that it’s OK? It is NOT OK!!!
      Read and learn before giving out imbecilic advice that will sooner or later damage someone’s pistol, or get them injured!!!

  80. Yes, most all newer Bushmasters have a Wylde chamber and will shoot both 5.56 and .223. The stamping on your rifle indicates this won’t be a problem either. If you want to double check, just call Bushmaster C.S.

  81. The 10mm and the .40 are NOT interchangeable! Either way, you’re are really asking for trouble. Both are high pressure rounds which will only compound any problems when it happens.

  82. Great article! Wish I would have read SOMETHING like this 5 yrs. ago. I bought an “DPMS Panther Arms Model A-15, It is stamped .223 – 5.56. HA! My first ABUNDUNT ammo purches was .223 55 grain. Every shot “stove piped”!!! I started using the NATO (FEDERAL) 5.56 62 grain and after more than a thousand rounds,,, they will STILL cycle thru as fast as you can pull the trigger / change magazines! .223,,,, PPPLLLTTT!!!

  83. I’ve got a “Ruger Mini-14,” and below that stamped marking, it is also stamped “Cal. .223.” These 2 markings are stamped on the top rear of the steel receiver, below and behind the rear sight. There is no .556 stamped on any where on the rifle. I got it new, aprox 35 years ago. Their website indicates mine (SN begins with 181-) was produced in 1979. I was told at the time I got it, that it would fire .223 and .556 I’ve never fired anything but .556 in it and never had any problems after many, many hundreds of rds. Mostly plinking and target shooting. It has never jammed. About 2 years ago, I read about never firing .556 in .223 rifles. I called Ruger and gave them the SN and they said that SN model would fire either cal. w/no problem. I don’t think they would kid me… certainly hope not, anyway. It’s a great little rifle.

    1. Please, let’s understand that Ruger makes firearms and knows what they are doing. Their marking on current Mini-14s says .223, but the manual that they print (see it on line) specifically states that every one of their Mini-14’swith the specific exclusion of their Target model is chambered for to accept 5.56mm ammo of any manufacture. I don’t know why that is so often the source of speculation. Please read their manual, and don’t worry. Ruger is not confused over their own product.

  84. Check out the CZ 527. Before I purchased mine, I asked, and CZ-USA told me that all of theirs (made in Europe) are NATO-spec, although they are marked .223.


      First off, the 10mm is a longer cartridge than the .40 S&W so it won’t even fit.
      Second the 10mm is loaded to much higher pressures than the .40S&W.

      There are however several handguns and a few rifles that can fire as many as 3 different CARTRIDGES, not necessarily different “calibers”. It’s not as simple as being only about bullet diameter.

    2. Let me a little more clear about this. A 10mm cartridge will not fit in a semi auto pistol than is made for .40 S&W. But even though a ..40 S&W will fit into a 10mm semi auto pistol, it is NOT advisable to do so. Both cartridges head space off of the case mouth so the shorter cartridge will only have the ejector holding it in place in the chamber. There are people who claim they do this with no problems but they are just asking for trouble, an accident waiting to happen.

      To my knowledge only some revolvers are able to fire as many as three different cartridges as far as handguns go, not semi autos. There are also lever action and bolt action rifles that are capable of firing more than one cartridge.

  85. All I believe you have done, Jerry, is muddied the waters further. I am an armorer. There are at least 3 main 5.56 chamber profiles of which one is a “long throat” NATO chambering, and there are several distinct and different chamber pressure specs used over the years. Some of the most recent ones (NATO) are about 10% higher in pressure and these are for use with heavy (long) projectiles. The Wylde chamber is basically a .223 body with a different neck and changes in throating dimensions to improve accuracy, all depending on how worn the reamer the manufacturer was using. The “slightly oversize” (compaired to the .223) chamber of the 5.56’s was done to accommidate dirty ammo and thicker case walls to improve reliability under battelfield conditions, along with the chrome lining. Some earlier 5.56 throating was no different than average .223 throating, but that has changed over the years. Also, some manufacturers in the commercial arena put their own “spin” on necking and throating if the operations are done seperately, with various claims for improvements in accuracy. Safe bet? Use 5.56 ammo with up to 62 grain projectiles in a 5.56 marked barrel only, and .223 in a .223 barrel. If the .223 barrel is marked for the faster 8 or 7 twist it may have a longer throat and then you can use longer projectiles in the 65 grain and heavier range. That’s the SAFE BET.

  86. You will be fine running 5.56 if the stamp on the barrel states 5.56 because if the math is done the 5.56 is actually .2234 inches witch is slightly bigger than the “civilian” .2330

  87. You could have put this on a sticky note – .223=.5.664. Therefore 5.56 is small enough to fit into 223 chamber / 5.56=218.90.

    As far as Hot goes, use the chronograph – my NORINCO / China Sports / Peoples Liberation Army .223 is 3300 fps. my Rem / Rem .223 is 2850.

  88. People who worry about this sort of thing have too much time on their hands. I have a DPMS AR that is stamped 223/5.56 and have shot thousands and thousands of hand loads, steel cased, 223 boxed, 5.56 boxed, 5.56 surplus, etc through it and haven’t had any problems. The truth of the matter is if you are that worried about accuracy, you are probably shooting a custom built bolt action, shooting hand loaded ammunition, and in a different caliber than 223.

  89. I have a Smith & Wesson model M&P 15, the barrel is stamped 5.56 NATO 1/9. I guess I am safe to use either round.

  90. I recently bought a Bushy C-15. The lower is stamped .223/5.56′ but the barrel is stamped 5.56 NATO .
    I assume from all I have read here is that it will be ok to feed it the 5.56 round????

  91. I submitted the article to my brother-in-law. Here is his response. Since I didn’t ask permission to post it, I’ll leave his name off.

    Lots of words to say not a great deal, and much of this seems a bit off the point.

    Chrome surfacing of chamber and barrel makes no particular difference in the comparison of 5.56 to 223; many rifles use an alloy rather than a chrome coating, which is better for long term durability, but the choice of chamber and barrel composition is its own topic.

    “Since 5.56mm Mil-Spec ammo is loaded hotter, it has higher chamber pressure.” This is true, but not highly significant to the matter. 5.56 ammo is built to reach up to 60,000 psi, while 223 Rem. ammo iis built to reach 55,000 psi, about an 8.5% difference.

    “Built to SAAMI specs, not Mil-Spec, the .223 chamber is ever so slightly smaller than a 5.56 Mil-Spec chamber. So when you shoot 5.56 in a .223 chamber, the case cannot expand as much as it would in a 5.56 chamber.” The shell neck needs to expand only enough to release the bullet without drag. After that, further expansion adds nothing. The rest of the case must enter the chamber freely, expand entirely to the chamber walls during firing, and then contract slightly for smooth ejection. An chamber of greater diameter only fatigues the case with little benefit to smooth operation. Slightly greater expansion of the case has little effect, but would very slightly decrease pressure. This again has little bearing on the comparison of 5.56 to 223 ammo or guns.

    He comes very close to the most important point when he says, “The second benefit of a 5.56mm chamber is that it also has a slightly longer throat/free bore area. In simpler English, that means that there is more space between the projectile and the rifling.” He then goes on to miss the point, saying that the longer throat prevents a heavier bullet, which is longer, from getting caught in the rifling and thus not loading or ejecting without a snag. No, it isn’t in loading and ejecting that the difference is critical. The main point is that a heavier bullet (over 62 grains) ceases to fit the specs for 223 ammunition. A heavier bullet within a single caliber is either made with something heavier than lead, or it is longer than a lighter bullet. This means that it either protrudes further, or it is loaded more deeply into the shell. Bullets loaded more deeply into the shell, pushed in beyond the base of the neck, need to be of a boat-tail design or they will undergo higher pressure before they ever leave the shell. In any event, a heavier bullet starts out more slowly than a lighter bullet, and the most extremely pressure-elevating thing that can happen is for a bullet to “slowly” try to press itself into the lands of the rifling rather than getting a good, running start and slam itself into place with adequate acceleration. Since a heavier bullet both begins more slowly and is also a longer bullet, this gives two good reasons for the longer throat (leade) to allow just that little extra bit of distance for the bullet to accelerate without restriction. This writer fails to point out this extremely significant pair of considerations of a slower, heavier start and more length of bullet to engage, which take things out of the specification for a 223 Rem. round. The basic difference is that 223 rounds are normally from 35-60 grains, while military service 223 and 5.56 are normally from 55-80 grains. Those are quite different cartridge classifications, once one gets beyond the crossover point, and special measures must be taken to give 223-compatible qualities to loads with heavier bullets, and vice-versa.

    Also, if the writer doesn’t like for manufacturers to say that a gun is made for both 223 and 5.56, claiming that it has to be either one or the other, then he again misses very important details. A standard military 5.56 barrel (which has fast, 1 turn in 7″ rifling) is made to handle a heavier bullet and of course uses the longer leade, but it is not designed to give accuracy to a lighter 223 round. A 223 round, first of all, will tend to strip somewhat in such a fast rifling spin because it starts out faster than a heavier bullet. A typical commercial barrel for both 223 and 5.56 has the longer leade, which makes it safe for a 5.56 round, but in recent years it has been given a tighter tolerance leade that improves the accuracy in the start of a 223 round. Also, it has rifling of 1 turn in 9″, which is middle of the road. This works well with 223 rounds, but it is not quite enough spin to stabilize heavier bullets in 5.56 at extended distances. I am not sure concerning the destabilization of lighter bullets at longer distances, but holes from hitting a target at 500-600 yards should reveal some bullet tilting if this is the case.

    So, the guy got paid for his opinion, but with all respect to his credentials I don’t believe he gives an accurate answer to the question that he chose to address. Meanwhile, thanks for sharing it; it has some things to think about, even if it is off track, and it allowed me to respond.

  92. You also have to take in to consideration, that the author has to err on the side of caution. He doesn’t go into the differences too deeply. The 5.56 has a longer lead, by about .060. That is the distance from the end of the casing, to the start of the rifling. As far as 77 gn. milspec ammo; I have never seen it. The different chamber pressures, is due to the use of different sensors, used at different locations, on the test gun, when they were measured. The slightly larger chamber size, is to reduce the amount of jamming occurances. Anybody who reloads, knows that there are small base dies, and large base dies. The small base dies are for semi-auto. These size the case just a bit smaller to reduce jamming. This does the same thing as a slightly larger chamber. as far as an upper receiver cracking; That was not caused by 5.56 ammo in a .223 chamber. The whole design of the AR was to keep all combustion stress and pressure, locked between the bolt, barrel, and barrel extension. This made it unnecessary for a heavy receiver, to control the combustion pressure, and to make a lightweight gun. Any cracked receivers, are more likely caused by incorrect buffers or springs, which allowed the bolt carrier to slam too hard into the receiver. Just my thoughts.

  93. I have dpms panther ar15 with mil spec barrell. About the accuracy difference,I was at the range just yesterday and was shooting standard federal 5.56 55 grain fmj, and buffalo bore .223 77 grain bthp from my ar. At 50 yards I robin hooded my bullet hole using each of the bullets one after another without moving my sights or adjusting my there isn’t an accuracy issue using either bullet from mil spec barrels..needless to say was very pleased with my rifle

  94. Well put together article, I have explained this information many time. But now I’ll just send them this article. If you buy an AR-15, get it chambered for 5.56 and when you reload rounds they will spec. out to 223. It’s a fun gun.

  95. I have a Colt CRX-16. On mag well it states .223/5.56. On Ruger web site it states you can use 223/5.56 ammo with the Ruger Mini 14, Can you do this with out damage to rifles ?


    dub roberts

    1. The mini 14 is not chambered for 5.56 unless you get the Mini 14 tactical. Which is the one with the flash hider/ muzzle break on the front and comes in both standard stock and ATI pistol grip stock.

    1. That’s easy. Just google “80% AR15 lower for sale” and you’ll see a whole bunch of places. Then you can get one from any manufacturer or retailer that hasn’t been raided by the BAFTE yet. We’ve had at least two raids here in the past 8 days that I know of and possibly more.

  96. this article leaves out allot of data .. for one it depends on the barrel manufacturer.. 5.56 MilSpec will happily accommodate a .223 and we are talking .0003 in differences in head space clearances . The hotter load of the ss109 penetrator is only about .08 grain charge with a mag primer which equates to average mismeasurements by common reloader equipment… unless you bought a “joes AR and sandwich shop” gun it will shoot either.

    1. ‘Scuse me for saying so, but the SS109 is a 55 grain FMJ, it’s the M855 that is the 62 grain steel core penetrator round. I’m sure you just got your numbers mixed up, right? 😉

      Also, the article was quite clear about being able to shoot .223 from a weapon chambered for 5.56 with no problem. But in general the reverse is not true with any degree of safety using an AR platform.

    2. It may have”been” the original for NATO, however here we’re talking about in the U.S., so let’s not confuse people.

  97. John he is not going to that. He only assuming they are being misleading. If he post it and is wrong than they will come after him. His article is just his opinion but states nothing new. If your rifle is stamped 5.56 it will shoot both, if stamped .223 Rem only use .223.

  98. So if we can’t trust the manufacturer’s website / Docs / Stamp on the gun then what the heck do we do? I own a Colt and a Mini 14 Ranch and was always told both are good to shoot the Mil-Spec stuff from both brands. Please tell us who we can trust to have the true 5.56 mil-Spec equipment. AND Tell us who you don’t trust…..Please


    1. Trust the manufacturer. Don’t trust anyone else!

      The manufacturer doesn’t come by this information in a vacuum, and he doesn’t rely on information blogs like this one to get his knowledge. He IS the knowledge. He’s the source of all knowledge concerning his guns.

      Two things must occur in order. (a) He must decide what specification reamer he will use. He might even make his own, according to SAAMI or NATO specifications. They are distinctly different, and he’s not clueless about the difference, and doesn’t need to refer to one of the experts on this blog. (b) He must “proof test” his gun before one of his testers wields a mighty hammer onto a stamped proof mark when the gun holds together under an INDUSTRY APPROVED PROOF LOAD that is available ONLY to gun manufacturers BY ammo makers (Federal, Winchester, Remington, etc.).

      The manufacturer (not a gun builder of parts made BY gun manufacturers), KNOWS the dimensions of his chamber reamer, and he KNOWS what proof specifications were purchased when he bought proof testing ammunition, whether it was SAAMI or NATO specification proof testing ammunition.

      Proof testing has been going on for centuries, since the advent of gun powder and the earliest guns, so that some King’s soldier didn’t have to worry whether a gun would fail under his chinny-chin-chin and loose the King’s battle.

      Rather than speculate about what a gun is built and tested to do, one simply confers with the maker of the fine barrel. And, if it’s not a proof tested barrel, it’s not a gun barrel. It’s a pipe that some fool might play with, but it’s not a gun barrel.

  99. Perhaps the author should identify the two manufacturers he mentioned in the article as being disingenuously misleading and/or uncooperative.

  100. I have a Bushy and it’s a “match Wylde chambering.” It’s stamped 5.56 / .223 on the receiver. I have some 5.56 ammo, but have only run .223 through it. I’m going to assume I can shoot either. The manual also states that it will take both 5.56 and .223, so I guess I’m covered.

    1. Look on the barrel. The barrel should say 5.56 NATO if it is mil spec. Which you can shoot both 223 and 5.56

  101. Can you provide the name of at least a couple of manufacturers that actually have a 556 chamber when they say so? You stated that you would not buy from the vendors that gave you email run around. Word of mouth for a reputable vendor goes a long way (good or bad!).


  102. I agree, the author forgot the best chambering of all. The .223 Wylde. Although I agree that a rifle chambered in .223 Rem should not be used for shooting 5.56 MM rounds, I disagree with the authors explanations of why. The 5.56 MM chamber does in fact have a longer throat than the .223 Rem. And, it is in part to allow heavier grain bullets. It is also in part to prevent the 5.56 round from exceeding the chamber pressures, since the bullet does not immediately make contact with the rifling in the barrel, it provides a bit of pressure relief on the chamber that a bullet immediately making contact with the rifling would not. In fact, if you take a .223 cartridge and a 5.56 cartridge, with exception to the annealing of the neck, there is virtually no difference in the measurements. Manufacturing variances account for the differences you are likely to measure. The primary issue that most people forget about the 5.56 Mil Spec chambering is that it is designed to handle Full Auto sustained firing. Thus it is designed to allow for expansion of metals from the excessive heat generated. That is the primary reason for the loose chambering of the 5.56 cartridge. When firing in full auto, the chamber will heat up enough to actually shrink several thousandths of an inch, presenting the possibility of a round lodging in the chamber due to shrinkage. This is the primary reason a fired 5.56 casing will expand more in the chamber. Not that the casing has to expand that much, just that the chamber is slightly larger, allowing the casing to expand more than in a .223 chamber, which uses tighter chamber for more inherent accuracy.

    1. A lot of us have been saying that but with no answer forthcoming. It was a glaring omission for an authoritative “professional” article.

  103. Anyone know whether the Ruger Mini Ranch rifle is chambered in 223 or 556? Unfortunately, the specs and marketing material contain the ambiguous “223/556” referred to in the above article.

    I checked one out at a Big 5 store this evening and the top of the receiver/chamber area is factory stamped “Ruger Ranch Rifle 556 Nato” (but the spec sheet only says “223” in some places and “223/556” in others).

    Can I rely on that stamp to mean this rifle is actually chambered in 556 and can safely shoot both 223 and 556 rounds?

  104. .223 Remington is the norm in civilian ar-15 style rifles? Hardly. Almost everything I see is chambered in 5.56 NATO. Sure you can find .223 remington specific rifles on the market, but the vast majority in my observation are chambered in 5.56. I think people should understand the difference and the article does a fairly good job explaining that, but I don’t think there is a big issue of people “accidentally” buying .223 remington rifles you almost have to go out of your way to find.

  105. Ok, so what about a barrel/chamber marked “Cal. multi”.
    Not looking to shoot match OR match grade but have purchased multiple 55 gr. AND 62gr. loads, both by Federal..
    Thanks Jeff

    1. You will not see a barrel/chamber marked “Cal.multi” – you may see a LOWER RECEIVER marked that way but NEVER a barrel. The Wylde chamber was not discussed and that may actually be the best option for all. If you reload, your dies will most likely be .223 Remington (small base is the type you should buy for AR shooting) so the situation is a bit more complicated and then nearly complex if you can get by with neck sizing only and still being able to chamber in your particular gun. Jumping the logical lines a bit here but if you want to consider EVERYTHING plan on lots of research and study.

  106. Also, not to be rude to ant shooter, but to compare an AR15 to an AK is apples and oranges to me. the AR is a finely tuned machine, and although durable the AK is stamped out of sheet metal and uses bailing wire for a trigger mech. i would not trade one of my AR’s for three AK’s.
    I guess I am just an american made snob… sorry.

    1. It isn’t your receiver that the round is fired in and normally a receiver isn’t stamped like that to my knowledge. If yours is I’d be calling the manufacturer. Your barrel may also be stamped but you may not be able to see it if the stamp is under the hand guard.
      AR lower receivers are generic enough that they will take either caliber upper receiver as well as a few other calibers when building the weapon.

  107. Jerry, I recently got a Colt M-4 .556 AR-15.
    Everything you said in your article and everything my research found out agrees. The .556 chamber is universal as far as .223 is concerned. Looking for a sight now. Love the rifle.

  108. Hmmmm I am not sure of this.

    Drawback #2: Heavy Bullets

    The second big drawback to a .223 chamber is shooting heavier ammo—77 grains and above. This is the preferred bullet weight for national match shooters and snipers. The problem is that those rounds are slightly longer than lighter AR ammo, so the projectile is sticking slightly farther down the barrel when you chamber the round.

    The problem becomes very obvious when you try to eject the heavier bullet-weight round from the chamber without firing it. This happens because the heavier projectile is slightly longer. On occasion, the rifling grooves may grab it when you try to eject it. The result is that you pull your charging handle back and the case comes off the bullet, spilling unspent powder on the receiver (and your magazine if you did not remove it first). As it ejects, you are left with a projectile in the barrel, and you will need a cleaning rod to knock it out. Then you will have a mess, and it is not fun—especially when you are on the firing line at Camp Perry competing for the national championships.

    The heaviest rounds that I have fired are in .223 and NOT 5.56. Years ago no one ever heard of the controversy of interchanging both calibers. Where was such a danger warning in the 70’s 80s, 90s? For many years I have shot both interchangeability and never had any problems SAMI standards being what they are and the 5.56 is supposedly loaded to higher pressures or allowed to be loaded to higher pressures. The heaviest round in 5.56 NATO I have fired is 63 grains…..I have not seen a 5.56 NATO round with a 77 grain bullet. As for 5.56 NATO in 55 grain ball. I have put it through Mini-14s, ARs in .223 Rem. and NEVER had any issues or blown primers or the separation of the bullet stuck in the chamber and separating from the case.

    As far as 7.62 NATO vs .308 Winchester….The .308 is loaded to higher pressure. My Ruger Gunsite Scout Rifle has no trouble feeding or failures with ether of those calibers.

    NOW telling me/us what I (and others) have done for many years, switching back and forth with 5.56 NATO and .223 in ARs and Mini-14s, is going to blow up in my/our face, separation of bullet and the case, powder dropping down into magazine, blown primers, cracking the upper receiver, or whatever issues. Have never me or anyone I know of involving thousands,Tens of thousands of rounds or more involving many thousands (or more)people, of shooting such. NOR have I (or anyone I know or talked to) ever heard of such happenings. I am speaking from REAL experience. Not reading some book or something off the internet that did not exist years ago.

    So how many of your catastrophic failures have actually happened and are documented?

    What are we going to be told NEXT… we cannot use 2.75 12 gauge shotgun shells in a 3.5″ shells chamber? We shouldn’t use .22 LR conversion kits in our ARs or Mini -14s or on our 1911s?

  109. No mention was made of the Wylde chamber offered with many reputable manufacturer’s AR platform rifles.

    From Wikipedia, the free encyclopedia

    The .223 Wylde is a proprietary rifle cartridge chamber with the external dimensions and lead angle as found in the military 5.56×45mm NATO cartridge and the 0.2240 inch freebore diameter as found in the civilian SAAMI .223 Remington cartridge. Rifles with a .223 Wylde chamber will typically accept both .223 Remington and externally slightly larger 5.56×45mm NATO ammunition.

    The .223 Wylde hybrid chamber was designed by Bill Wylde of Greenup, IL to exploit the accuracy advantages of the .223 Remington chambering without pressure problems or compromising the functional reliability of (semi) automatic weapons like the AR-15 family when using 5.56×45mm NATO military ammunition.[2] Coincidentally, it shoots the relatively long and heavy 80-grain (5.18 g) bullets commonly used in the sport of Highpower Rifle Competition very well and is one of the preferred chambers for that use. The Wylde chamber is used by a few rifle manufacturers who sell “National Match” configuration AR-15 rifles, barrels, and upper receivers.

  110. Thank you for clearing this up, I went to a local sporting goods and asked and was given much the same advise and decided that a 5.56 sporting rifle would become part of my varmint collection. Now the problem is finding a sporterized bolt action rifle chambered for a 5.56… The one I looked at was not something I would own, I think it was a Mossberg…I do like my 223 and it became a go to for varmints because the expense on my all time favorite 22-250 is becoming outrageous….
    If there is a manufacture for a decent 5.56 bolt action I would like to know.

    1. In response to: “… the expense on my all time favorite 22-250 is becoming outrageous….”
      I empathize with you and other shooters feeling the pain from exorbitant ammo prices or, worse, unable to find your fav caliber at all. The solution: Reload! Seriously consider investing a couple hundred dollars up front — press, dies, powder, primers, bullets … and recycle all that brass you previously kicked aside. I currently load 9mm Luger and .45 ACP pistol rounds … .280 Remington/7mm Express and 5.56 NATO/.223 Remington rifle cartridges … AND, specific to ONTIME’s heartburn, I have the means to reload 22-250 cartridges when I run out of my stockpile of factory rounds. I admit that there is a significant commitment of personal time to reload. But it’s like a favorite hobby, with fiscal rewards compounded by a feeling of independence/self-reliance (“I’m no longer hostage to ammo shipments to and prices at Walmart, Gander Mountain, Cabela’s, my local gunshop, etc.”). For example: my 9mm Luger handloads work like a charm in my Glock 17 and cost me less than 16 cents per round versus double that (or more) for factory ammo. Think about it, bro!

  111. If we can’t trust what the manufacturer says, or the spec sheets, or even the side of our lower receiver, then how can we know which AR’s are 5.56mm and not .223?

  112. Great article and extremely well written. While I theoretically can’t reach out as far as .223 my 7.62x.39 AK shoots everything and anything I put in it and has never, knock on wood stock, had a cartridge come apart or get stuck. Unlike the AR platform the dirtier the weapon is the smoother the operation seams to get. Most of the AK surplus ammo available has corrosive primers, this simply means that after a day of shooting if you don’t have time to do anything else shoot some gun scrubber and then some oil down the barrel.

  113. Do you mean the shoulder angle? The charts that I have seen states that the shoulder angle is 23 degrees on all of the chamberings

  114. Jerry,

    The article is misleading some manufactures such as Bushmaster and Colt put 5.56 NATO/ 223 Rem on the side of their rifles for a reason. This does not mean it is both Mil spec and SAAMI spec. If the rifle is chamber 5.56 NATO than it will also fire 223 without any problem that is all it means. Do you really think a company like Bushmaster (Freedom works) and Colt would want that level of liability by mislabeling their rifles. The bottom line is if it is chambered for 5.56 you can also use .223 Rem. If it is chambered for .223 Rem only than do not use 5.55 in the rifle.

    This is from Colt site for the Military M4 where they say 5.556/223 as well.

  115. Jerry,

    The article is misleading some manufactures such as Bushmaster and Colt put 5.56 NATO/ 223 Rem on the side of their rifles for a reason. This does not mean it is both Mil spec and SAAMI spec. If the rifle is chamber 5.56 NATO than it will also fire 223 without any problem that is all it means. Do you really think a company like Bushmaster (Freedom works) and Colt would want that level of liability by mislabeling their rifles. The bottom line is if it is chambered for 5.56 you can also use .223 Rem. If it is chambered for .223 Rem only than do not use 5.55 in the rifle.

  116. The author failed to give examples of ARs that are mil spec 5.56. That would have been nice. Otherwise the article only restates what is pretty much know about the 5.56 verse .223. Nothing new here

  117. Mike the military AK74 uses a 5.45 not 5.56 and yes it will go through soft body armor just like all rifle rounds will that is why they have rifle plates over their soft body armor. There is an AK74 made for the U.S. market chambered in 5.56 but it has not really picked up a following. I believe Arsenal is discontinuing it because of poor sales.

  118. I don’t understand why such an informative article omitted the Wylde chamber, simply put it is the best option especially in the stainless RockRiver , I have tried them all and the rock is the best I m o. No wonder why all federal law enforcement are now Rock River equipped.

  119. I own quite a number of AR15’s and have always checked to ensure they were 5.56 before making the purchase. For me, there is no other way to go. As far as the comment about AK’s. It arguably may be true that the 7.62 X 39 is a slightly better round, however the poor ergonomics of the AK are not worth the questionable superiority of the round.

    1. When using iron sights, I prefer the ergonomics of the AK over the AR. My only real complaint with the AK is the selector lever.
      As a jeep rifle, I choose the AK for a number of reasons, not the least of which is the fact that with soft point ammo, it is legal for hunting. The AR would require a second upper, mags and ammo.
      The AK is easier to operate, easier to strip and clean, and mounts naturally to the shoulder, similar to a shotgun. The AR, OTOH, has a buffer tube that extends straight out the rear of the receiver, forcing the shooter to shoulder the rifle in an unnatural manner, with the toe of the stock high in the shoulder pocket with a poor cheek weld.
      Operating the charging handle on an AR is an ergonomic nightmare, compared with many other systems.

      When the AK jams out of battery, the top cover can be removed and the weapon serviced. When the same happens to the AR, it is necessary to remove the stock and buffer tube, with the risk of losing small parts.

      Bad stuff happens if foreign matter is in the gas tube or buffer tube of an AR, when fired. A catastrophic failure of the AR locking lugs allows a bolt carrier to be projected directly toward the rear of the buffer tube, where your face and shoulder are. The AK does not put moving parts next to your cheek, and when it does fail, the bolt carrier slams the rear of the action and the comparatively light top cover flies up and away.

  120. The AK-74 is chambered for 5.45 x 39

    And perhaps I’m wrong but check your barrel. If it’s stamped 5.56 that’s what it is, if it’s stamped .223 then that is what it is. Usually stamped near the muzzle

  121. Not to be rude to the .223 or 5.56 people, but why even waste your time with either when the 7.62 is by far the superior bullet and the AK or the finer milled American copies are far superior weapons whether you are talking about range, penetration or dependability?

    Now, if you want to talk about the 5.56 Soviet “stinger” round fired by the AK-74, then you might have something to talk about, as that round will penetrate our military issue vests!… 🙁

    1. My error Ray….. Gotta read before my “stupid” finger presses the “send”… Thanks for the head up….. That said, I NEVER want to be on the receiving end of that round no matter what kind of an issued vest I am wearing… 🙁

    2. Just a guess here, but maybe because what you’re talking about was not the point of the article at all?

  122. I’ve owned an AR-15 SP-1 .223cal since 1970 and have fired both .223 and 5.56 for over 44 years with no noticeable problems to this date! Is it possible that the early ARs were built better?


  123. i have spent a lifetime under the impression that the distance between the chamber and the beginning of the rifling is called “freebore”
    Roy Weatherby freebored his rifles and it allowed the bullets to build up speed without creating too much pressure. When others chambered custom rifles for the Weatherby cartidges some did not allow freebore and they could not achieve the velocities without excessive pressure.

  124. Correct me if I’m wrong , Is there a differents in the degree of the neck also , 1 being 17 degrees the other 18 degrees .

  125. I’m with Ben on this. Where does the Wylde chamber fit into this? Are you referring to a “match chamber” as a Wylde chamber? Your article does clarify a lot of the “myths” of the 5.56 or .223. But why not simply refer to the chambers as most people do. .223 SAAMI, 5.56 NATO, and .223 Wylde?

    I hope when you tackle the 7.62 NATO and the .308. You just tell the basics. The NATO round has a recessed primer the .308 round does not. Therefore when running .308 in your NATO chamber you run the risk for slam fires. I understand your articles have to be a certain amount of words. You could always just use some filler. Like half naked woman holding awesome guns????

  126. Great article. No doubt, you can shoot what you want but make sure the chamber is 5.56 mil spec compliant. Other wise, be a safe rifle owner and only shot the .223 shell.

  127. My bolt-action .223 was made in Europe. When I asked the US branch of the company about this issue, I was told that most, if not all European made rifles are made to the NATO (5.56×45) standard, and that mile was safe for either.

  128. It seems to me you left something out. At least you didn’t mention it and I’m curious as to why? This would be the “Wylde” chamber which has become very popular among both match and varmint shooters. It eliminates many of the problems you mentioned above and allows the use of the heavier bullet weights as well.

  129. The simple answer is to buy an AR- 15 chambered in 5.56. You can then safely shoot .223 or 5.56 in your weapon. There is a lot of information out there on this subject and some is not correct. Buy a rifle chambered in 5.56
    you will be much happier and safe. I am not a gun smith or trained armorer, just an educated shooter. You have to decide what is best for you.

    Big Joe

  130. Thanks for the information. It forced me to go back & check specs on my own rifle, to make sure it is chambered for .556, and not just .223

  131. Reading the write up I have the same question regarding the Wylde chamber that is inscribed into the side of my PWS ar lower. It was explained to me by the manufacture as the perfect in between. Although Samuel explains that we just ask the manufacture, the end of the article states that you cannot always trust and should not trust what the manufacturer says.

  132. Excellent article – explains the match chamber variations as well as the old .223/.556 question. I took the bull by the horns a couple of years ago and decided on the 5.56 chambering. Being an old hand-loader and overly technical guy, I have studied about everything in print concerning the issue(s.) I recently machined an adjustable head-space gauge to precisely characterize my AR15 chamber. If one uses “store-bought” ammo within the guidelines stated in this article, one should never have an issue. Interestingly enough, chamber and ammo specs are not always precisely within the SAMMI or even Milspec ranges. My own chamber headspace (well known brand-name AR15) is actually .003″ shorter than commercial (or military) specs. However, I have yet to measure any commercial or military ammo that wasn’t short enough to easily fit the chamber! Even head-space gauges can vary between manufacturers. Go figure!

    All this is of some concern to those that re-load for the AR15. Factory ammo (only) shooters need not be concerned. If you are having chambering or extraction issues with “storebought” ammo, by all means contact the firearms manufacturer and/or the ammo manufacturer!

  133. A milspec chamber should say 5.56mm NATO. The FN m16 are standard military issue they read FNMI. MP 5.56 NATO 1/7 I know this because I am holding it.

  134. Thanks for the Article. What would be really nice is some more info like:

    1. Which popular Rifles available from CTD are 5.56 and which are .223.

    2. Does the same apply for Bolt Action Rifles? Can I fire 5.56 in a .223 hunting rifle w/o problems?

  135. If you want to find out what chamber is your barrel all you have to do is read the information that is stamped on the barrel. It will tell you not only what chambering but also the barrel twist. Don’t go by what is stamped/engraved on the receiver, go by what is on the barrel. Also as mentioned in the comments a few times the.223 Wylde chamber was left out…why? It’s been around for more than a few years and is pretty well known. It’s a great compromise between the 2 offerings with benefits of both.

  136. Great write up and nice to reaffirm what I have been told before at CTD. You have a great business and glad to bring my business there. Yes your pricing is sometimes way off but I understand it’s hard to keep up with all of that.


  137. To complicate the issue even more my Winham Vex uses the .223 Compass Lake match chamber. The leade is shorter than 5.56 but not as short as .233, and the angle at which the bullet emgages the rifling is different. I have great results so far with either ammo.

  138. I am waiting for an answer about the Wylde chamber. I have two AR15 and had both built with Wylde chambers to avoid these problems. Please send me an answer. I would like to know if I have made the correct choise or have to refit my rifles. Thank you Dennis

  139. Good article! I always thought that 5.56 mil spec was just a higher quality round! The article left me hanging a bit as to how to make sure the AR I buy is in fact chambered in 5.56 and not .223!

    1. Barrels should be stamped by the manufacturer. It will show the caliber and twist rate. The lower receiver should also have a manufacturers stamp showing the caliber.

    2. The Barrel will be stamped with either .223 or 5.56 NATO

      The stamp should be on the top of the barrel clearly visible.

  140. The author should really do some research. The diameter of the two chambers are the same, at least according to drawing I found from Rifle magazine of the SAAMI specs and mil-spec for the 2 cartridges. The overall shape of the two chambers are the same too, which makes sense given that the overall shape of the brass for the two are exactly the same according to spec. The only difference is the throat, which is considerably shorter and sharper in .223. That makes perfect sense since Remington originally designed to .223 to shoot 40 grain bullets. You need that short throat for the best accuracy, which is why most AR-15s don’t shoot the really light bullets so well. It’s the short throat that can cause 5.56 to go over pressure in a .223 chamber, and it’s the reason that no AR-15 that I know of uses a standard .223 chamber. Nearly all of them use a Wylde chamber, which is a compromise between the two. The throat in a Wylde chamber is in between the two so as to not let .556 go over pressure but still preserve the accuracy of the .223.

  141. I don’t know if I agree that ‘most’ AR-15s are chambered for .223 Remington (the proper designation). It seems most I look at are stamped .5.56. My own DPMS Oracle is stamped .223/5.56. Now, whether that marking is accurate or not is another matter.
    Also, a huge point of contention is the ammunition available. How many times have I seen boxes marked ,.223/5.56′? And how many times have I come across boxes of commercial ammunition labeled .223 Remington and filled with brass that has a Lake City headstamp and no caliber designation (meaning it’s 5.56). Mind you, these don’t come from the likes of Remington, Winchester, or Federal, but the ‘second-tier’ producers.

  142. I was aware there was a slight difference between the two rounds as far as the shape and size of the round. When I bought my AR I made sure that it could use both types of ammunition. I wish that I had read the article first. Thank you for a well written article that brings clarity to the issue.

  143. I have a Smith and Wesson M&P AR-15 I just went and took a look to verify. The barrel says “Nato 5.56-19” I have only used .223 through it, and have not noticed a lack of accuracy. can you tell me… is the 19 the length of the bullet in mm. also since the barrel does not say .223/5.56, that Smith and Wesson is not trying to pull one over on me. I can steal that can of ammo without worrying about shooting issues. Thanks.

  144. Your article left out one chamber available for the AR 15 rifle, have you forgotten about the newer chamber being currently offered? .223 Wylde? It’s designed to shoot both. 223 and military 5.56 reliably and more consistently than the other chambers. But I’m sure that you would get the best accuracy out of a match chamber with custom or match quality hand loaded .223 ammunition for that rifle.

  145. It is as simple as contacting the manufacturer of your firearm. The possibility of liability will be the guide to their offering you the correct information about calibers. I contacted the manufacturer of my M-15 in writing, via email. The answer was forthcoming within minutes. Just dont guess. Go to the horse’s mouth. It only takes a few minutes to get it right.

  146. Where does the Wylde chamber fit in to this? I was under the impression that it could shoot both rounds but was slightly tighter and therefore theoretically more accurate than the 5.56 chamber while not having the issues of shooting a 5.56 round through a .223 chamber. Is this true?

    1. The Wylde chamber is like the match chamber the author was talking about. It may be exactly what he was describing actually. It’s a long throat .223 chamber that will prevent 5.56 ammo from getting over pressure (that’s what actually causes popped primers) but not so long as to degrade accuracy. It’s a good compromise as it allows the safe use of 5.56 ammo without significant loss of accuracy when using .223. The vast majority of AR-15s being made now use the Wylde chamber for exactly that reason.

    2. The Wylde chamber is an interesting compromise that has the longer throat of the 5.56 but is tighter around the walls of the case. It should be fine for 5.56.

      If you would like to check a chamber Michi-guns sells both a guage and a reamer that are easy for most anyone to use. If you only have one or two rifles to ream I would suggest a group buy as the reamers are somewhat expensive. They are very high quality though and will cut numerous chambers.

  147. Sir, thank you for this extremely informative article. I am a military trained armorer, so I fully grasp your ideas and concepts. I just wish future weapons owners would take a few moments to do their research and speak with reputable gunsmiths who can inform and guide them prior to their making a purchase. I know I did, and did not regret it one bit. Mark Tipton, a gunsmith and friend, broke the whole scenario down in a way that I understood the bullet may be the same but the cartridge, and its make up are not. Please keep writing these informative articles.

    Very respectfully,

    Donald Newman

  148. Well written article. Explains the difference between the two chamberings for the ammunition, but does not identify the “jump” for what it really is.

    As explained, the slight difference between the distance that the projectile has between the brass, and the riflings is called the “jump” and that small “leap for mankind” (pun intended) allows for just sufficient expansion of the gases driving the bullet to keep from blowing primers.

    Caution is advised when choosing a rifle. Know enough to “ask” for, and get the most versatile weapon for your purpose. Better to be really safe on this one than have a cracked upper and/or blown primer at a really really bad time.

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