.300 AAC Blackout: Speak Softly and Carry a Big Stick

The next big thing in AR-15s may not be a piston driven operating system, or a fancy internal coating that requires little lubrication, or a new rail system for attaching accessories. The next big thing just might be the caliber that the AR-15 is shooting. The perceived issues with standard 5.56 NATO ammunition have led to the development of many competing “alternate” calibers for the AR-15 rifle. Calibers such as 6.8 SPC II and 6.5 Grendel promise better stopping power and increased effective range compared to the old 5.56. But I think the hottest new caliber of all is the .300 AAC Blackout, and here are a few reasons why:

1. .300 AAC Blackout is a .308 bullet inserted in a cut down 5.56 casing. The .308 caliber bullet may be the most common bullet diameter in the world, so this gives the .300 BLK unmatched selection in bullet types and easily available casings that can be quickly made with an inexpensive case trimmer and a cordless drill. This caliber is already super easy for handloaders, they can just trim 5.56 brass down to the correct length, create the .30 caliber shoulder with a resizing die, and insert their favorite brand of .308 bullet. Done! No waiting for another special run of bullets or casings to be made, and no paying high prices for specialized components. My friends and I make more .300 BLK brass every time we go shoot our 5.56 AR-15s—it just isn’t trimmed and sized to .300 BLK specifications yet!

2. Using 5.56 casings means standard magazines work and you get standard magazine capacity. 6.8 SPC II and 6.5 Grendel both require specific magazines different from each other and different from the Standard Nato Agreement (STANAG) AR-15 magazine. These magazines are not nearly as common, are not made by as many different manufacturers, and of course cost a bit more. On top of that, you lose capacity in those calibers, down to 25 rounds instead of 30, because their casings are fatter and take up more space inside the magazine. Barrett is the only manufacturer at this time making an extra-long 6.8 SPC magazine still holding 30 rounds. Since .300 BLK uses 5.56 casings, standard followers work just fine and capacity remains the same. Folks are shooting .300 BLK through Magpul Pmags and even Surefire 60 round mags with no problems at all.

3. The only difference between a .300 AAC AR-15 and a 5.56 AAC AR-15 is the barrel. Again, because 5.56 casings are used, you don’t need to swap out the bolt or buffer spring or anything else. Although buying another bolt isn’t a big deal for many shooters, bolts made with larger faces to accommodate bigger casings often have durability problems. 7.62×39 bolts in particular are notorious for always breaking at the same weak point. The AR-15 bolt was originally engineered with a certain amount of metal in the locking lug area for a good reason, and removing metal there to accommodate a larger rim weakens it. One solution is to just move to the much larger and heavier AR-10 platform—if you don’t mind lugging that heavy beast around. But anyone capable of swapping barrels on an AR-15 can convert their 5.56 NATO gun to .300 BLK with no additional changes. Of course, AAC, DS Arms, Black Dawn, and other companies offer complete uppers in the caliber—attach the upper to your lower receiver and you’re good to go.

4. Up close, .300 BLK hits hard. The supersonic loads for this caliber are more powerful than .30-30 or 7.62×39, and more accurate due to the .308’s more efficient bullet design. AAC claims that the .300 BLK is more accurate than 5.56 out to 300 meters, but that’s not the whole story. Chopping the carbine barrel down to submachine gun length is now the biggest trend in AR-15s for military, law enforcement, and even civilian shooters. It is well documented that the number of NFA applications to register short-barreled rifles with the BATFE has skyrocketed, and police and military buyers are looking for  lightweight, handy carbines with barrel lengths in the 10-inch range. The problem is, 5.56 NATO loses a lot of its stopping power with a short barrel because it depends on velocity for terminal effectiveness. A 9-inch long .300 BLK barrel gives the AR-15 nearly 25% more muzzle energy than a 9-inch barrel shooting the 5.56. Even with a plain 16-inch long barrel, the .300 still features about 15% more muzzle energy than 5.56, but where this caliber really shines is when you’re shooting a short-barreled rifle. If you’re looking for a long-range caliber, 6.5 Grendel definitely has the edge, but most real world engagements with carbines take place within 300 yards, right in the wheelhouse of .300 BLK.

 5. .300 is super quiet. Unlike 5.56, subsonic loadings that still cycle the AR-15s action reliably are easy to make. A 220 grain .308 bullet and a minimal amount of powder will result in a velocity of around 1000 feet per second. At close range, these 220 grain rounds really thump, and the real kicker is that using an AAC suppressor with them in a 9-inch barrel brings the sound level to only 125 decibels. That’s quieter than an MP5SD shooting 9mm rounds, and much quieter than a MK23 pistol shooting .45acp rounds. Statistics charts and YouTube videos don’t do it much justice—you have to be there and shoot one of these rifles with a “can” attached to realize that this 220 grain bullet is nearly as quiet as a silenced .22 pistol. For those of you who won’t ever get a supressor, this is a non-factor, but for folks who have discovered the joy of legally shooting quiet guns, the small powder charge and large bullet subsonic combination is tremendously exciting.

If you look at it one way, the .300 AAC Blackout gives you more stopping power than 5.56 NATO without having to change anything but the barrel on your AR-15. Put another way, you can have that extra stopping power in a package the size of a 9mm MP5SD, but even more quiet! Add in the fact that this caliber uses .308 bullets and reworked 5.56 NATO cases for maximum parts commonality, and you have a big stick that speaks very softly indeed. Daniel Defense, CMMG, Armalite, Bushmaster, Smith and Wesson, and Sig Sauer, and Wilson Combat are among the companies building complete rifles in .300 BLK now. Over 60 companies have announced that they are going to build product lines around the caliber. At SHOT Show 2012 it seemed like everyone was “jumping on the .300 BLK bandwagon.” AAC’s .300 BLK “Honey Badger” PDW concept has early adopters clamoring for more. Right now it looks like .300 BLK is 2012’s most popular new caliber, and the next big thing in AR-15s.

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 (16)

  1. This is an old post but it came up on a Nov 2015 marketing blast, so I thought I would add this. The Lee Precision Lead Mold TL-309-230-5R produces 220-230 grain bullets depending on alloy that work great in 300 BLK and if your powder coat them there are no leading effects. If you use wheel weight lead and recycle 223 brass you can load these for less than 7 cents apiece. Just another nice survival attribute along the article idea.

  2. “The supersonic loads for this caliber are more powerful than .30-30 or 7.62×39, and more accurate due to the .308’s more efficient bullet design.”
    This is not true…. 7.62×39 has about a 200fps velocity advantage over a supersonic 300blk load. Bullet composition is similar. The 30-30 is no slouch and has roughly a 300fps velocity advantage and can use spire type bullets in non-tube guns, or utilize polymer tipped bullets. If we go up to the 170grain bullet range 30-30 will dominate the 300 blackout due to powder volume restrictions and push the exact same bullet 400fps faster!
    300 blackout excels when you go to subsonic loads, here it does pull away from 7.62 and 30-30. The real strength is in its ability to be so versatile. But making generalizaitons that it is “more powerful at supersonic” and gains due to bullet design are a moot point since they all can utilize the same bullet in the supersonic range. 300blk benefits from being chambered in a more accurate platform (AR-15). As opposed to 7.62X39 (AK/SKS) and 30-30 (Leverguns). However these are generalizations, as 7.62×39 and 30-30 are both found in bolt guns and other platforms.

    1. True or not true its a matter of load data. If I could stick a firing tables in here you could clearly see that with an equal muzzle velocity for subsonic 123 grain AK loses big. For Supersonic the best AK round, a 123 gr Hornady 7.62×39 Z-max BC 0.295 (G1) with a muzzle velocity of 2380fps from a 20″ barrel bolt gun gets whipped by my lowly powder coated 230grain Lee tire weight lead 1550 fps round in a standard 16″ AR.
      Z-max AK Energy 995 at 175 yds., 619 at 350 yds., Lee Lead 998 and 819
      If you really want to see performance check this lee lead bullet from my 300 Win Mag 992 ft-lb at 1,200 yards

    2. I’d have to disagree with you on the 30-30 all the ballistics charts I see are with a 24 inch barrel where as 300 blackout is with a 16 inch barrel that’s over 8 inch’s of barrel and I do believe the 300 is actually underloaded and not quite to the saami spec

  3. In CQC the most important consideration in my opinion is foot-pounds of energy in the target or stopping power if you will. The 300blk has it’s station but for close quarters I personally prefer the Kriss Super – V in 45acp. Very little recoil due to new mechanics. Unless one wants to bust engine blocks or the like – I will stay with the 45acp 230 grain HP. Very high speed gives you penetration. The right mass plus the right speed is CQC heaven.

  4. @Comment by Matt Thats a LOW CLASS comment.

    For me the choice is simple, the 300 aac is the right choice especially if you already have a ar15 its a easy barrel swap. I have a quick change system so I can go from 5.56 to 300 aac in 30 seconds.

  5. As a military brat& yes born on base. It just seemed natural to join the USMC. I did read several stories confirming the 9mm just didn’t do what it was hoped to do. Their are old stories and new testimonials where 9mm didn’t have it. I’m a strong believer in the 45. It just works & does it well. Elmer Keith pointed out that a diameter of 41 caliber was an ideal combination of knockdown & penetration. I believe the 1911 in 10mm, 40 Corbin, or 400 super; could all be the ideal defense/close quarters rounds in a pistol. I own multiple pistols in 45 & 10mm. They both are accurate. My 10mm kimber seems to be able to hit 24″ targets @ 100 yards. The recoil keeps it from being a service round. I love my 45’s & carry them. Just wished military would man up an use the 10mm or the 45. The service arms all need to get muzzle comps on then to hold the three round bursts to stay closure together. Being an Armorer for several years I know a simple & easy fix to Excessive muzzle climb. This thread started with the 300 AAC blackout brown. So I feel it fitting to address some of the 300 AAC characteristics and evaluate those. The 300 AAC is capable of having Excellent knock down at very close ranges with a short-barreled M-16 with a lot less noise. I would desire to hear from anyone about the accuracy of the 300 AAC in a short-barreled M-16 or short-barreled pistol with 9 inch or 12 inch barrel lengths. The 300 AAC with short barrels has been stated that after going 9″ down the barrel it really does not gain any more velocity which really makes it the ideal CQC round. All to often we become blinded when shooting shorten barreled carbines do to the excessive muzzle flash which is caused by unburnt powder normally. An advantage for the 300 AAC is more than just knockdown, quietness, & accuracy. Muzzle flash is also lower because all powder is used up within the first 9″ of barrel. I would desire to read from anyone using or has ran tests. Thank you all and please forgive me if something really doesn’t make sense. I can only see about one and a half lines on my phone.

    1. StanUSMCborn: I agree that our military needs to go back to .45ACP or up to 10mm however, until we stop letting women into the service, I’m afraid we will always be stuck with a semi-anemic caliber.

    2. I’ll throw a $1000 on the table that my friend, a woman, will out shoot you in any caliber. As for being weak I can also set up a “training” session with Ronda Rousey. I’m sure being the big bad MAN that you are you would kick her ass in a heartbeat. But i digress ignorance, like a cockroach, will life for ever.

  6. Thanks for the informed response. I am coming around to your line of thinking. After seeing the effectivenees if my .30-30 ” plinking load”, the light bulb is coming on. 165 grain leas bullet at 900 fps is far more damaging than I imagined. Horsepower doesnt necessarily mean torque, does it?

  7. Rand… You really think stopping power is determined by velocity? You need only look at the tried and true 100 + year old .45acp. It has a stopping record that cannot be questioned and has one of the slowest center fire pistol velocities. A heavier bullet if always the way to go in close quarters combat and medium range (as the 300 round was designed). I’ve seen firsthand the lack of stopping power from SEVERAL well placed 147 grain 9mm +P and +P+ rounds. I was in a S. American country in the late 80’s, @ 26 years old and the members of my protection team called me “Old Man” because I carried a 1911. They all rode high on the 15 round Berretta 92 9mm bandwagon, bragged about their ‘firepower’, reliabity, etc. One day prior to our departure we were involved in a prolonged firefight and we didn’t have access to our MP5’s or M16’s. I was having to put people down that had several 9mm rounds in them already, I’m sure you will find similar stories that will back my experience as well. The moment we reached US soil all but one of my team members switched to .45 1911’s or the S&W 1076.

  8. 30-30 is not 200-300 fps faster. It is about 100 – 140 fps faster for the same bullet weight. The reason why you think it is 200-300 fps faster is because you are quoting a 24 inch barrel length for 30-30 and a 16 inch barrel length for 300 BLK.

  9. Stop saying the 300ACC Blackout is more powerful than a .30-30. It isn’t. In 110 grain .30-30 is about 200 feet per second faster. In 130 grain, it is about 300 feet per second faster.

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