Firearms

Four Reasons Why the Operating Rod AR-15 Might be the Worst Gun Idea Ever

BCM bolt carrier group

There’s a persistent line of thinking among certain circles in the shooting community that goes like this: Since many reliable firearms have an operating rod, replacing the direct impingement gas tube and bolt carrier group of the AR-15 will make it more reliable. This is a false equivalency, with its roots based on the old wives’ tale that direct impingement guns are inherently unreliable.

A semi-truck has 18 wheels designed to drive long distances. Wouldn’t it be awesome if your commuter car did too? Perhaps, but probably not. It’s the same way with AR-15s equipped with an operating rod. Here are four reasons why you’re almost always better off sticking to a high quality, direct impingement rifle:

Operating rods tend to introduce more problems than they solve.

The AR-15 rifle is more complex than many shooters believe. There is far more to the function of the system than a simple “gas blows the bolt carrier back.” When the volume of gas heading toward the receiver enters the carrier key, it actually pressurizes the area adjacent to the gas rings.

BCM bolt carrier group
Starting with quality parts is the best way to get a reliable rifle. Not by adding the unneeded complexity of an operating rod.

This pushes the bolt forward, and keeps the entire assembly locked until pressures have dropped to a safe level and the brass case has contracted. If you remove this influx of gas by replacing the gas tube with an operating rod, you have a far more abrupt and violent system. The operating rod acts like a hammer, and bullies the bolt carrier group backwards in a most impolite fashion.

But that’s not the end of the piston-driven AR-15’s troubles. The battering ram-like rod forces the entire carrier down at an oblique angle, which causes “carrier tilt.” This tilt erodes the area of the receiver just in front of the buffer tube, and can cause major problems over time.

Furthermore, the additional reciprocating mass of an operating rod is much harder on gas blocks and bolt carrier groups, especially in simple conversion kits. Granted, many companies (such as LWRC) have perfected the overall system and removed most of the early problems. However, this comes at an added cost.

The direct impingement design works just fine. Really.

…and if it doesn’t, something is wrong with how your rifle is built.
If you still think of a standard AR-15 as inherently unreliable, you need to get with the times. Properly built guns, such as anything from Bravo Company Manufacturing, Daniel Defense or FNH, USA will be as reliable as the day is long.

Arms makers like the ones above listed prove that the old, tired argument of “The direct impingement rifle defecates where it eats, and that’s bad!” just doesn’t hold water. But, you don’t have to spend over a grand just to get a reliable rife. Doing your research and purchasing reputable parts from the get-go will go a long way toward owning a bombproof gun.

Dirty AR-15 bolt
Here, we can see harmles carbon buildup on the tail of the bolt

As with any rifle (with or without an operating rod), proper maintenance is essential. Keeping both types of gun properly lubricated with a proven product such as FrogLube or M-Pro 7 is a requirement for stellar performance under all conditions.

Spare parts.

In the extremely unlikely (read: impossible) failure of a standard gas tube on a semiautomatic rifle, a replacement can be readily found nearly anywhere gun gear is sold. That’s because the direct-impingement gun is the standard. Plus, it’s easy to keep one or more on hand very, very cost-effectively.

This isn’t the case with operating rod-based rifles. All parts are proprietary from manufacture to manufacturer, and are always more expensive than a simple gas tube or spare bolt and carrier. Plus, you’ll need multiple specialized parts just for one rifle to cover all of your bases. And good luck finding those spares if the world abruptly decides to end, and you need to bail out.

Weight and complexity.

Rifles with an operating rod always add more weight and complexity to the overall gun, with few, if any, tangible benefits. In most cases, you’re better off sticking to the tried-and-true direct impingement methods.

Much can be said about light rifles, and doing everything possible to keep the overall weight down. If your rifle can be built without sacrificing reliability, why go with a heavier option? Adding comparative complexity with an operating rod is simply unneeded.

Even if it could be proven that an operating-rod equipped rifle was objectively more reliable than a properly built direct-impingent gun (and it hasn’t been proven), most users don’t shoot enough to have an actual need for the extra reliability.

AR-15 gas tube
This simple part is the key to the AR-15’s reputation for reliability

For the average shooter, a direct impingement gun is far more than good enough.

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So, is that the end of the story with AR-15 operating rods?

All that being said, there is one area where an operating-rod driven AR-15 makes sense: With ultra-short barrels (10.5 inches and under, typically) and a suppressor. These unique conditions can cause issues for a direct impingement gun when used heavily, due to the greatly reduced dwell time of shorter barrels, and increased backpressure from use with a suppressor.

Rather than fundamentally changing the design of the AR-15 and adding multiple parts while introducing a new set of problems, simply set up your standard barrel length direct impingement gun for success, and shoot the snot out of it with quality ammo.

Do you have any first-hand experience with AR-15 reliability, in either piston or direct impingement formats? Tell us about it in the comment section.

[disclaimer]

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 (174)

  1. I’ve been using my 1st AR, a 10″ SigP516 for about 2 years suppressed. So far, the only ammo I’ve been able to run reliably is Hornady 75gr TAP SBR. Everything else has inconsistent ejection patterns, about 1-2 failure to close the bolt/mag and sometimes an empty will jam between the bolt and chamber with a live round also chambered. My Springfield Saint Edge 16″ has non of these issues with any ammo.

  2. Sorry folks, I forgot to say: Gas piston rifles are usually used in harsher
    conditions compared to regular or normal situations where the gas tube rifle
    was designed to operate…

  3. My dad was in the U.S.Army, he played with Special Operation personnel. He found out that the normal troops have the gas tube! Spec Ops use the gas piston operated rifles today! A few reasons why a piston was found to be better? 1. Unburnt residue from the gunpowder with the gas tube is vented back into the upper receiver that builds up and causes the gun to jam. 2. The gas piston rifle vents behind the front sight. 3. The bolt carrier operates smoother and longer between cleanings, while lubed properly. 4. Gas piston rifles operate underwater! 5. You get the gas tube submerged, you have to break the water seal of the bullet and brass from the chamber before you may fire the weapon, or it may blow up in your face! 6. The U.S. Army found this out during Vietnam testing of the first few versions of the M16…
    With all the possibilities for building a custom AR style rifle or pistol today; depending on what type of rifle/pistol you need, you have the option for the gas tube or piston! The market has a monopoly on the gas piston operated bolts; when more become in demand, the prices may come down and part options may increase!

  4. It’s funny that people still insist on calling it “direct impingement” when it can be (and has been) conclusively demonstrated that the AR-15 does NOT function via direct impingement. A real DI gun has basically a flat bolt carrier face, and a blast of high-velocity gas, a jet, escapes the gas tube, impinging on the bolt carrier face and imparting energy to it. An AR-15 bolt carrier is a cylinder, the end of the gas tube is a piston: it’s a reverse piston-operated setup, with the cylinder moving and the piston staying stationary (like a spigot mortar). The only thing it shares with a DI design is that it pipes the gas directly back into the receiver, instead of placing the piston way out over the barrel and transmitting the force via a long steel rod. It’s like someone shortened the long gas piston/op rod on the AK, installed the piston inside the block under the rear sight, and used a long gas tube where the piston tube is now, to pipe the hot gasses back to the receiver. Well, that and they flipped it around so the cylinder moves with the bolt carrier and the piston stays in place, but that’s getting to far into it. Anyway, an AR-15 isn’t a direct impingement: it’s just not. That’s a plain fact. But people insist on calling it that anyway.

  5. The gas key doesn’t vent gas, it simply meets the gas tube and lets it travel into the bolt carrier where the back pressure forces the bolt forward. The gas is actually vented out of the two holes behind the bolt that you see on a standard bolt carrier where the vast majority escapes, only a small amount actually remaining inside the gun and less making it into the receiver.

  6. Why can’t we have an extended bolt carrier key that extends through the front of the receiver and into the handguard where it could vent the gas there instead of inside the receiver and it would still be gas impingement with none of the ill effects of a piston.

  7. This article had me convinced until I got to the part about the gas tube never failing. Only reason being, I put 150 rounds through my AR for two days in a row in ninety degree weather. Upon returning to Alaska, I found that my gas tube had stopped generating enough pressure. This caused consistent short-stroking of the bolt carrier group. The way I found out that it was the gas tube is when Alaska Ammo replaced it with a new one for $17. Since replacing the gas tube, I have fired 420 rounds without a single malfunction.

    At the time of bringing it back to Alaska, my rifle had fired 1,300 rounds during its lifetime. Is the AR15 reliable? Absolutely. However, I have learned, as with any machine, the AR15 must be kept well-lubricated and below a certain temperature. I don’t know what that temperature might be for an AR, but I know that I fired five magazines in less than five minutes with an ambient air temperature of ninety degrees. After having fired the fourth magazine, steam was rising from under the handguard, and I could barely keep my hand on it. Even then, I fired one more magazine. This, as I now realize, was abusive to my rifle.

    In conclusion: keep it lubricated and keep it cool.

  8. Im tired of the misinformation that gets spread around. And sorry about the typos.

    1 Stoner did not design a direct impingement gun. His design was self described as an expanding gas system which does in fact utilize a piston. See that picture of a bolt? It HAS A PISTON INTEGRATED INTO IT!

    Direct impingement throws up fouling all over the breech face and chamber area, permitting excess carbon, corrosive materials, and mechanically corrosive action(the gases themselves with particulate moving at nearly supersonic speed) to affect the breech and chamber area of the gun. Causing increased wear, potential for stuck cases, and a generally dirty gun in this and the reciever area. A problem with direct blowback guns as well.

    The ar is little better, it initially diects gas behind the breech face, but it throws up every bit of that gas in to the reciever area behind the carrier. Which naturally finds its way forward, and fouling up the area it intitially avoided.

    Also, the gas pushes the piston forward, which though opposition causes the carrier to reciprocate, the carrier moving backward causes the bolt to rotate to unlock, allowing the bolt to travel rearward with the carrier. It you look into it, there is very little benefit to this design, other than a very mild reduction in pressures on the breech face, and a small reduction in recipratory forces, which btw can be another argument for unreliability and finicky action.

    2. The long stroke design does cause a tilting load on the carrier as it must be either mounted above the breech (AK) or below (garand) which can cause wear to the sheer loading surfaces of the gun (carrier/reciever rails) and with the AR that can be a problem because the carrier is made out of steel (neccessary) while it rides on aluminum load surfaces (stupid) thats why guns like the SIG556 were designed to be long stroke from inception use steel uppers at the expense of weight. I guess only mech engineers and metallurgists understand how crappy aluminum is. And how dissimilar metals should be avoided in shear load scenarios.

    3. The gun is lighter, and so is the bolt and carrier assy, but simpler? HELL NO! There are more parts and narrower gas passages taking a longer path through multiple parts. At least long or short stroke keeps all the expanding gasses forward of the action, taking a MUCH simpler and shorter path, venting quickly and reducing fouling in the gun. Is the AR simpler? No. More reliable ABSOLUTELY NOT easier to clean? Nope, harder.

    4. The gun is lighter because it uses less robust parts, these lighter assemblies and inferior materials under load make the gun more difficult to tune with a wide variety of loads and external factors such as humidity and ambient temperatures. Under optimum circumstances, there would be less felt recoil. Unfortunately we dont live in a sterile world.

    Also, the teeny bolt locking lugs on the ar upset me, they could and should be more robust, they probably wanted less rotation of the bolt to allow for quicker lockup and unlocking. But i see these as flimsy in an important area of the gun and more suceptible to sticking due to fouling.

    In summation. If you want a “simpler lighter gun” the vz58 is A simple gun which runs clean, is over a lb lighter than an akm, uses short stroke piston design. Shoots REALLY flat, and is robust in every way with fewer moving parts that are all made of STEEL! not to mention the .30 caliber round which is better for everything except punching paper. Guys, .223 aint a good round for anything else, its not even good at killing people. It is a “casualty producing round” it wounds well, not as good for killing (It doesnt “hunt”) and the short stubby light projectile has a poor ballistic coefficient compared to say, 5.45×39 or .220 swift. And it splatters at long ranges making it ineffective past say 300m? Dont get me wrong, there are alot of ppl and other creatures dead from .223, some at great ranges, but the same could be said of .22lr. Either way its irresponsible to hunt with a round like that. Even with the heavier, slower moving hunting rounds.

    IF you want AR ergonomics, and prefer .223, but dont want to sacrifice EVERYTHING ELSE, buy a SIG or a SCAR. Its a better gun. And you range queens wont mind the extra weight, you militia members, nut up and stop complaining about lugging around an extra lb or 2, do some pushups and cardio and increase ur strength while losing some of that gut.

    But im sure many will disagree

    1. @Grant, the AR-15 is plenty simple in its stock configuration. If you find yourself perplexed at its design, you’re probably an idiot and would be better off peeling potatoes or cleaning the head. Pop some pins, pull out the bolt carrier, soak in CLP, scrub with toothbrush. Bam. Unless you’re engaging in thousand-round firefights regularly (extremely rare even for the people who get in firefights for a living) you will never have your weapon lock up on you from carbon and unburnt powder. It just doesn’t happen, and cleaning your weapon takes a total of 10 minutes. It doesn’t have to be polished to a chrome, it just has to be scrubbed and lubricated.

      Watch Iraqveteran8888’s AR-15 meltdown videos in which he tests both a DI AR and a piston AR and the results may surprise you. The DI AR-15 made it into the upper 700 rounds count before the barrel exploded, and that’s because it was made of 416R stainless steel, which sucks at handling heat compared to 4150 CMV. You may also be surprised to find that the piston AR he tested mushroomed at the operating rod, warped the bolt carrier and scratched the upper up. That’s 3 parts in need of replacement as opposed to 1 which had nothing to do with the operating system.

      The AR-15’s stock pseudo-direct impingement operating system is amazingly reliable, and if it were so fragile as you claim, tier one operators who get to pick and choose their gear wouldn’t still be using it to this day.

      The VZ58 is neither as modular nor as accurate as the AR-15 and uses a milled aluminum receiver, not “all steel”. It has a top-open action that allows an extreme ingress of filth and debris to enter the action, as opposed to the AR’s precision, tightly closed dimensions that prevent filth from entering IN THE FIRST PLACE.

      Your assessment of 5.56 displays an astounding level of ignorance. It’s perfectly adequate for killing people, has been for years. M855 was designed to penetrate a Soviet helmet at 1000 yards and is capable of exactly that, and produces a wicked wound channel which much greater velocity than your cherished 7.62x39mm. It was the effectiveness of the 5.56mm round that caused the Soviets to want to mimic its effects in the 5.45×39 which has a lesser ballistic coefficient, by the way. Are you among the school of dogma that believes 9mm to be inadequate, as well?

  9. I have owned a Colt M4 Carbine for a good while now. Have put only a couple thousand rounds through it, all at the range, and have had zero FTL’s or FTF’s. Average session is about 200-250 rounds, green tip, soft point and plain ball rounds. It is dirty when I clean it but not near some described on these sights.
    Guess I’m lucky but I know the piece is built well.

  10. My experience with gas impingement tube on the AR 10 and 15 is growing.
    I have read many accounts about magazines causing cycling issues. I have always used magpul and see no need for change with them.
    One problem I do see that is another topic is bolt catch issues. There is without a doubt a blue print deviation problem between manufacturers. I can run them wet or dry the parts off and still have issues. Read some articles stating the holes for the springs of the bolt catch were too shallow and there seems to be some misunderstood tolerances that stem from the DPMS platform to the Aramlite platform. In any case it’s a pain.
    Enough of the bolt catch back on track.
    Gas impingement systems are fine. Have never had a doubt about it. They are a challenge for the hand loader. I do believe that hand loading rounds for these platforms will educate you as to what your rifle requires for correct cycling and accuracy. One persons load data for their rifle-barrel twist combo does not mean it will work in your rifle that very well may have the exact twist rate and barrel length.
    I started out with a Colt Light weight Carbine. 1:8 twist 16 inch barrel. I played around with all types of loads. 77 grain 80 grains so long you couldn’t load them in the magazine I tried all I could with this rifle and it made reloading an AR seem easy. I jumped in deeper and ordered a JP Enterprises. 223 Wylde. Now the Wylde is supposed to be a chamber that holds more pressure and I suppose it does. The first time in tried one of my tried and true loads suited for my Colt I got a refresher course on rifle cleaning. It spit a primer out and I was pissed. I spent all night cleaning this exotic piece. Don’t get me wrong. This is one nice rifle. I can set up at 200 yards and rapid fire into a 12 inch target and hit 20 out of 20 most times .
    This rifle just demands a lighter load with different powder to cycle properly. Less powder to make the same muzzle velocity equals less money saved.
    These rifles demand individual attention.

  11. 16 inch barrel, mid length gas system, H buffer, extra power buffer spring. Feeds all day with any ammo. ANd SMOOTH!!!

    1. I have an AR15 that I purchased in 1985. It has a direct gas system. I cound not get it to shoot more than 5 consecutive round at a time. I did everything I could think of. I am a Viet Nam vet and thought I knew about weapons especially AR15s. At the range one day I was having my usual trouble with feeding. The man next to me saw my troubles and ask if I would like to try a magazine from his rifle. The magazines were from Mag-Pul, all of mine were metal from the weapons manufacture. The Mag-Puls’ worked well and I had not even thought it might be a magazine problem. I use strictly Plastic magazines and run the rifle wet with oil. I have never had anymore problems of any kind. You’r never too old to learn.

    2. @Bob:

      Can you explain more about running it wet with oil? I have never done this before. Like are there any DO’s and DON’T’s?

    1. The HK91 is about 10 pounds with a full magazine. Mine does a great job and NEVER fails to do what it is supposed to do. Yes 7.62×51 does weigh more than the 5.56 but I know I can trust it to put down whatever it hits. No need to worry about clean burning powder as it runs fine clean and filthy!

  12. Parts availability and weight are the only valid points made here. The d.i. design DOES crap where it eats and that’s a plain fact from the first one to the last one, at least the piston design gets the bugs wrung out (carrier tilt?….thing of the past.)

    What gets me is the attempt to focus on the failure of a gas tube as a problem pointed out by the piston community….it’s a stainless steel tube. It’s going to “function” i.e. crap where it eats until it jams, which it will do if not kept clean or run wet which is something that traditionally hasn’t been done. Now you need food grade lube because of the petroleum mist that’s going to be swirling around your head!

    Let’s not overlook the fact that these points of contention are like the 7.62mm vs 5.56mm AR argument, what people forget or just plain don’t know is that Eugene Stoner’s original design was in 7.62 and likewise he was working on the piston driven AR when the design was sold to Colt.

    Recent remote sustained firefights have proven (again) the weak point of the d.i. design but one couldn’t legitimately call the design a failure, it’s light, accurate, modular and serviceable in 90 out of 100 situations. All the cherry picking of negative points (or positive) of both designs to prop up one design in favor of the other is getting really tiresome. I have both, I shoot both and I am convinced that my LWRC piston driven 6.8mm spc is the epitome of the AR evolution but in a shtf nightmare scenario it would be foolish to run into a, defend the Republic/minuteman scenario with it when the military and police use the d.i. system like my Bushmaster M-4 in 5.56.

    Shoot what you like, like what you shoot and pray our service members are triumphant in combat regardless of what design they are defending our Republic with.

  13. There are better guns and operating systems out there, but let say you really have to go into battle, what gun are you more likely going to be able to pick up ammo and parts for in the field?

    1. As far as ammo, the .308/7.62 is a very common everywhere so I believe I’ll be good on that aspect. The HK-91 side of it, I make a habit of carrying the most common repair parts such as replacement rollers, a spare bolt assembly but not much else. The 91 is hard to beat!

    2. @US Army (retired):

      As you may remember, you already helped me with advice last week. But now I have more questions.

      Would you say that your HK-91 is closer to AK technology, or AR technology? My guess is AK.

      Can you please look up, here on Cheaper Than Dirt, the Century Arms C308? I like the price on this baby!! Is this patterned after your HK-91, or do you see significant differences? Even if you’re not a fan of Century Arms I would appreciate your comments.

      Here’s where I stand…..I’m blown away and shocked by all the drama and complications of AR’s that have been discussed on this forum. I’m tempted to sell my DPMS LR-308 AR-10 (most likely a DI system) and buy this Century Arms C308 and put cash in my pocket, knowing that I also bought into more reliable technology.

      Any opinions from anyone else would be appreciated. This is real dollars and cents for me. My gun budget is limited.

    3. Neither one, the HK and it’s predecessor the CETME operate on the delayed blowback roller locked system. Simply put the bolt is held in place after a round is fired by the two rollers that hold it in the locked position until the pressure has dropped to a safe level. The rollers unlock and the remaining gas pressure, assisted by flutes in the chamber which assist in “floating the spent casing and cause the bolt to move rearward ejecting the spent casing and picking up a new round. Is it dirty? YES! Is it more reliable that a DI system? YES! I have fired many rounds before cleaning mine but I have not had ANY malfunctions with my HK91. The Century Arms C308 is a good deal. Another upside is the availability of magazines at a VERY reasonable price. Aluminum mags go for about $2-4 per and steel mags for about $3-5 per. I personally have 40+ magazines, mostly 20 rounders but a couple of 10 round and a couple of 5 round mags. I hope this helps and if you are like me you will love shooting it. It just gobbles what you give it!

    4. @US Army (retired):

      Thanks for all the excellent info!!

      How would you rate the HK91 accuracy versus AK’s, and versus AR’s?

      I am SOLD ALREADY on either the C308 or C93. All I need to do is put 2 or 3 guns up for sale, and when 1 sells, I buy a C93 or C308 (I still need to decide which one).

      Thanks much for telling us about your HK91. That’s why I hang out here. I learn things and become aware of guns that I had no idea existed.

    5. Mine has an 18″ barrel, which I would recommend for the C308 (7.62). I don’t believe the C93 (5.56) is available with an 18″ barrel, not sure.

      My HK91 I used to drop a deer last year and paced it off at 300 yards. I aimed at the top of its shoulder and hit it about 2″ lower which broke the spine. It dropped right where it was standing. I have a rail for scopes and I used a Simmons 3-9x40mm standard hunting scope. I sighted it in to be dead on at 200 yards. I won’t shoot at a deer over 300 yards unless it is standing perfectly still. I also have a Ruger bolt action 308 and if I am hunting where there may be a need for more range I’ll use it due to the 22″ barrel.

    6. @ US. Army (retired).

      The longest-barrel available for the HK93 (C93) is a 41V50 556 Match Grade Barrel of ~26-inches in length with a 1:9 Right Hand Twist…

    7. @ US Army (retired).

      H&K has a 26-inch 1:9 RHT Match Grade 556 41V50 Steel Barrel if your Interested for about $499.99…

  14. Regardless of what make or model of gun you have, if you clean your gun after every outing it will give you a life time of service. I have never seen a properly maintained gun fail. If you think buying a piston gun will get you out of cleaning your gun it will fail too.

    1. I totally agree with your comment. I made some comments based on actual combat experience in Vietnam. The M-16 was not properly vetted, i.e. it was put into service as a front line weapon without the necessary testing and it cost good men their lives. I have had an aversion to it since. Yes the problems were resolved but I won’t but one. I’ll stick with my current delayed roller locked H91 clone. I am saving up to get an M1A, which is a operating rod weapon. I trained in the Army on it and when I was handed an M-16 I went to the troop armorer and swapped it out for an Ithaca 12 ga. riot shotgun. I was on a tank, I had no need for the M-16 but the shotgun was excellent if I had to dismount.

    2. I was in Vietnam for 2 tours in 1969-1971. I got a lot of trigger time and I never had a problem with the M-16. I preferred a Stoner, but the M-16 was just fine. I also liked the 12 gauge. If you are worried about reliability, I would just get an extra DI upper to slap on your lower. I have put tens of thousands of rounds through weapons with and without an operating rod. The only failures I ever encountered were of my own making.

    3. Old Navy, Welcome home brother! I was in Vietnam on my first tour (1969) and got injured due to an RPG about 5 months in. Spent time in/out of hospitals for nearly 8 months, finally got medically cleared and immediately got orders to go back. Arrived Aug, 1970 back to the same unit (3/5 Cav) and finished a 12 month tour. Got nicked by shrapnel two more times but nothing serious. Being on a tank I found the M-16 to be unnecessary. That is why I preferred the 12 gauge. I now own a HK-91 (7.62) that is probably as dirty firing as the M-16 but it is not DI. The beast will shoot whatever I feed it and clean up is very easy. Never has any FTF, FTE or other malfunctions. It IS VERY hard on the spent casings. I had a deflector spot welded on the ejection port and I can now reload my spent brass!

  15. Since Adams Arms has been using a slightly unique bolt carrier, several years I think, that system has been flawless. I see zero carrier tilt and zero bolt wear after 3,000 plus rounds

    I can not conjure up a reason to use the DI system going forward. Even the weight issue is essentially solved with their low profile light weight and adjustable piston gas block.

  16. Changes are not always a necessity, some things are best the way they were originally designed, take for instance the Colt 1911, it is essentially proven design never changed, just minor stuff and better materials. The bolt action rifle designed back at the end of the 19th century is essentially the same as a modern Ruger or Remington. A new design has to bring substantial value over a previous one for it to be adopted.

    1. @Javier or James H:

      Can either of you list 3 to 5 popular brand name AR-15’s that use the rods?

      I see above in the article that Daniel Defense is one that doesn’t have rods. Is that correct? Regarding the other 2 listed with Daniel Defense, I’m not familiar with Bravo, and FNH is usually too expensive, so if you can please name any popular brands that don’t have rods, that could help me select an AR-15.

      Bottom line, I’d like to get one that is inexpensive and I can shoot a lot without breaking or jamming. I will never get into the inner workings of an AR-15 as much a many people here do.

    2. Patriot Ordnance Factory (POF) , Adams Arms, Syrac, Heckler Koch, Ares Defense. The author of this blog is just a troll trying to make people think he is knowledgeable about pistons and d I systems, when it sounds like he doesn’t know much about either one.

    3. I went with the Sig 516, and one of the reasons was the piston action. I am NOT a self proclaimed AR expert but it seemed to me from a pure mechanical stand point and that there are several very successful piston rifles like the AK, that if executed correctly it would be a better way to go….

    4. loufish,

      I see from your previous post you have opted for the Sig piston. I think that is a good choice. I would have suggested Sig first, then LWRC and finally, the S&W. Other than that, I like the kits on a “homemade” AR or M4 because you can customize it to your liking. The advantage of one of the factory pistons is that they are birthed as such and are dedicated to the PI. Good luck with your rifle.

      Sincerely, JH

  17. Let me try this from another perspective….I kind of see the piston system as having several advantages mostly not venting dirty gases into the BCG…Many have stated that the DI system works so well that it hasn’t changed much since it’s introduction in the 60’s….I think the the piston system has been refined enough to take over the DI…BUT just like our TV’s were we had a standard 480 line of display in “service” for 50 years…the new standard of 720/1080 (HDTV) was the next evolution of TV’s but what to do with all those older TV sets….My theory is that with so many DI rifles out there with standard spec parts, nobody wants to introduce a newer updated system. Once you take away the interchangeable parts issue (Which I do agree is a valid augment) there comes a time when you move up to the next thing…..

    1. What we do with the old TVs is we retrofit. Well, maybe not so easy with old televisions but, with the several number of piston kit suppliers out there, those who want a piston rifle can have one fairly easily and at reasonable cost.

  18. Regarding the SAFN-49, interesting gun which I did not it existed. I checked on the web and the SAFN-49 or FN-49 is a gas piston operated gun, by contrast the MAS 49/56 does not have a piston, the gas tube fits directly into the bolt carrier which makes it a very simple gun. In fact field stripping the gun only involves 5 parts: The bolt carrier, the bolt, the recoil spring, the recoil spring housing/cover and the firing pin….that’s it.

    1. Javier,
      You may have misunderstood… my meaning was the FN49 is essentially the same as the AR piston rifle, not like the MAS. The MAS and FN are similar in their respective caliber choices and deployment purposes and they are both semi-automatic as opposed to most military bolt action rifles of the time. I had choices when I purchased my FN49 just after I obtained my C&R license and was looking for surplus rifles for my collection. Both the MAS (French) and my FN (happens to be the Egyptian version) are sought after collectors guns and are becoming more rare. The FN is a little more expensive but are just about equally respected. I chose the FN 49 over the MAS because it is a piston rifle, hence my mention of it in response to your mention of your MAS 49. Another similar rifle of the period is the SVT 40 which is also a piston rifle of which I own as well (1940 Tula). Probably more information than you wanted.

  19. Allow me to clarify, I was attempting to explain how the so called direct impingement system works, not a gas piston system. In essence both are gas pistons, just the piston is located in different places.

    It would seem to me that most people believe that the force that pushes the bolt carrier backwards comes from the gas key and “my dissertation” was attempting to dispel that notion. Granted, it might be over the top to speak of masses, momentum conservation and forces of acceleration, but hopefully a picture will be worth a thousand words, go take a look at the following link:

    http://stonerclone.blogspot.com/2013/04/ar-15-gas-impingement-system-animation.html

    There you will see very good animation where they clearly show how the gases are siphoned from the barrel, to the gas key and into the rear face of the bolt (where the sealing rings are). The gas key job is to convey the gases into the chamber formed by the bolt rear face and the carrier. The gases create a force that pushes the carrier and bolt in opposite directions, the only movement that can happen is for the bolt to move rearwards.

    If you have access to a MAS 49/56 you will see a true direct impingement system, the gas tube fits into a corresponding round hole in the bolt carrier’s body. This hole is blind so the pressure that accumulates there pushes the carrier and subsequently the bolt backwards. The rest is well known.

    The only and only point I am attempting to make and hopefully I am coming across is that the force that pushes the carrier back comes from the inside of the bolt-carrier group, not from the gas key, and that makes it no different from a traditional gas piston system. The main difference is where the gases are vented out.

    Javier

    1. Javier, There is no argument as to how the bolt is manipulated by the operating systems of ARs and M4s, e.g. where the gas comes from where is goes and what it does when it reaches the gas key on the BCG (or the piston chamber on the GP). After that, the functioning of the BCG is fundamentally the same for the DI and the GP. I don’t have a MAS but I do have a SAFN-49 which is essentially the same. I think we have beat this poor horse enough. Thanks for the exchange.

  20. I’m very confused on this topic, partly because I currently own a DPMS AR-10 and 2 AK’s, and have not been thinking about AR-15’s for a long time. Yet I want to re-enter the AR-15 market to get into substantial noise suppression.

    So can someone please list 3 popular AR-15’s that HAVE the Operating Rod, and 3 popular AR-15’s that DON’T have it? That way I can get a better feel for what I would want to buy.

    1. Sig 516 patrol,Any LWRC, Ruger SR-556 are all piston guns. Armalite, RRA, DPMS all make pretty nice DI guns. In my limited experience(I own both types) the biggest difference is maintenance. The piston guns definitely run a bit cleaner. There is still carbon in there, but I assume the reduced temp. helps keeping it from hardening.

    2. @Charlie:

      THANK YOU for answering my question with clear, simple and practical information. This is the kind of information I was looking for!

  21. I have a Stag piston upper on my AR. Only issue was I had to install a stronger extractor spring as I was getting failures to extract. Once I did this, I have 100% reliability. Super clean bolt carrier even after shooting hundreds of rounds. I don’t have to run my AR “wet” any more with lube which sprays black oil at times. I have about 2000 rounds through my piston AR and no problems whatsoever. I understand that GI may be more accurate but out to 200-300 yards I can still easily hit a man size target with an aimpoint optic.

  22. Newtonian physics uh?
    Let’s look at it. Newton’s third law of motion states: For every action there is an equal and opposite reaction. This means that the bolt is under a force which is equal the one exerted upon the carrier but in opposite direction. With the bolt locked onto the receiver and the rest of the gun, the only possible motion is for the carrier rearwards, the mass of the bolt combined with the rest of the gun is clearly larger than the carrier’s, and since there is a person holding the gun (hopefully) the total mass associated to the bolt is even larger, the only relatively free mass is the carrier’s. So in a way it is correct that the bolt is pushed forward, but it is only a reaction of no consequence to the locking of the bolt which is indeed locked onto the carrier by way of the lugs and slots.
    As the carrier continues backwards it causes the bolt to rotate due to the cam action, the bolt disengages from the receiver and the carrier continues its travel backwards until it reaches a stop which causes the bolt plus carrier to move backwards as a one, extracting the spent round and then stripping and feeding a new one on the rebound.

    The AR system is indeed a good one, and in essence it is a piston driven system as most of the unlocking force comes from the area around the sealing rings, which is a piston in the strict sense of physics, there is also a small amount of force that comes at the top of the carrier where the gas tube connects with the carrier, but because the cross area is relatively small only a small fraction of the total force will come from there.

    1. Javier, I think most of us who use, maintain, repair, and appreciate all types of operating systems understand newton’s physics. Your dissertation is probably a little over the top for many of us. Not to be condescending, I just think your point could have been made a little more simply. E.g. the force of the gas as the round expels it past the gas port exerted on the piston rod through the chamber forces the carrier group rearward. As it does so, the extractor grabs the spent case by pinching it by the rim, pulls it out of the chamber, and the ejector kicks it out the ejection port. The bolt carrier group proceeds to compress the buffer spring which, on decompression, forces the bolt back across the magazine striping off the next round and forcing it into the barrel insert for firing the next round. The direct impingement system does essentially the same thing but uses gas directly into the gas key to move the bolt carrier group. As you say, for every action there is an opposite and equal reaction. Sorry if I was rude with my simple question but I had to read your reply several times.

  23. I have used M4s throughout my career and have had few issues with them, but I have had issues. A direct impingement is much more dirty and has much more heat in the chamber, and these 2 things alone can make a firearm fail it’s cycle of operation over time or during a rapid rate of fire. I look at a direct impingement like this, it sh*ts where it eats, and to me that is never a good idea.

    The carrier tilt like stated above has been fixed in most all piston ARs. so that is fully fails now.

    The weight, well I look at it this way, the M110 I have used weighs over 15lbs, my piston AR10 is 13lbs and I have a bit more on mine.

    Now about the rob failing, it is MUCH more likely for the bolt rings to fail in a DI firearm then the rob in a piston AR.

    People can argue all they please, but the facts are out, pistons are the future of ARs, Many elite operations use piston ARs now and haven’t looked back.
    Will the direct impingement disappear? No it will always be around, but it isn’t ever going to be as reliable or clean as a piston.

    If you still have any doubt, one company has had a piston AR10 being tested for failure for a few years now. It has 68.580 through it, with only 33 malfunctions. I don’t know many other firearms able to do such a feat, and I have no doubt no DI could.

    At the end of the day go with what you like, at the range both DIs and pistons will do just fine, but I will only trust my life to my piston ARs

  24. The M-16 series has direct impingement, which makes them require frequent cleaning of the upper receiver and bolt assembly. The more reliable AK-47 series uses a gas rod.

    The SRC Reliabolt carrier has a beveled rear bolt area which eliminates the “carrier tilt issue.

    My Piston-rod-modified AR is as reliable as an AK now and a snake through the bore cleans it just fine now.

    No brainer for me.

  25. There are over 100,000 negative comments on the internet over the last 10 years BUT, they are all concerning the “Short Stroke” gas piston system. The “Long Stroke” system solves the ‘Tilt” problems. I invented a L.S. piston system for my AR-15 back in 1981 after I got out of the Navy. I revised it last year to fit inside the long skinny hand guards that are currently trending due to use by 3-gun competitors. The system uses commonly found parts for future replacement needs. My new company will be called Divergent Arms.

  26. I will always value the opinion of those who have used the weapon in question to defend the Republic. The true test of reliability is actual combat deployment in various hell holes around the world. I am told, in combat, there are times that one has scant time to clean a weapon. That being the case, it would seem that a well-engineered op rod system would be better suited to real world conflict. Designs like the HK 416 and the SCAR heavy come to mind. For civilian use and law enforcement, a DI system is fine although I would still coat the bcg group in NP3.

  27. I have both piston and DI AR’s. I don’t think the writer has much experience with piston operated AR’s. A piston rod fails about as often as a gas tube breaks. My piston rifles operate cleaner and cooler. One had over 5000 rounds, the other 2500. I use quality factory ammo and have never had a failure in either weapon. I am sold on the piston rifles.

  28. One historical fact that everyone has missed, maybe because they are not old enough to have been there, back in the days of the Korean War, or “police action”, if you prefer, the Korean troops were of a smaller physical stature than the American soldiers, and could not handle the size and weight of the M1 rifle, nor its replacement, the M14 !
    So part of the design criteria that Stoner was directed to include, was a smaller lighter rifle with less recoil than a .30 cal weapon had at the time.
    This was a political decision imposed by Washington on the criteria for a new shoulder-fired weapon !

    1. Now we have a new situation, which is not jungle warfare– the middle East, where shots are made at mucher longer distances, we don’t have Aisian partners in these conflicts whom we are supplying with weapons, and the 5.56 cartridge at the shooting distances required is showing its shortcomings.
      I have been very interested in the results of tests using the 6.5mm Grendel, when compared to the M4 or even the M14 or M1A. It seems this cartridge will outperform both of them, but due to the budget constraits put on the military by our current politicians, we have a “make do” scenario being played out! What a shame..

  29. The writer is writing with feeling, not total facts. The rod tilt has already been fixed in today’s models, plus the FACT that rod action rifles run MUCH CLEANER and WITH MUCH LESS HEAT than the standard AR/M4 platform…… the only disadvantage to having an op rod rifle is that you are now beholden to the maker of that rifle for several parts.

  30. The author of this article should check his facts. He wrote:

    ” This pushes the bolt forward, and keeps the entire assembly locked until pressures have dropped to a safe level and the brass case has contracted”

    First of all, the bolt is locked and the piston inside the carrier actually pushes the carrier backwards starting the unlocking process. Secondly the whole purpose of the gas entering the chamber between the carrier body and the ring sealed back site of the bolt is precisely to allow the process of rotating the bolt to disengage from the receiver. Physics 101 buddy!!!

    In all truth the AR-15 direct impingement is in reality a piston operated gun, just that the piston is an integral part of the bolt. The only truly direct impingement is the MAS49/56, which is not only very simple, it works very well.

    1. Javier Guzman: A common misconception.
      The gas pressure does indeed push the bolt forward. It is less mass than the carrier so it indeed moves forward with higher acceleration than the carrier is driven backward. Think of it as the two being driven apart from each other, the lighter piece moves faster. The bolt is limited in how far forward it can go, but it is enough to unseat the bolt from the breech allowing it to rotate freely and unlock as the carrier is driven backward. An ingenious system designed to exploit basic Newtonian physics. One area that can cause problems is if the shockwave from the gas, the bolt mass, the carrier mass, and rotation cam are not appreciated as a carefully designed system. Fortunately, if these parts are faithfully reproduced and adhere to design dimensions, it works even if the builder does not appreciate the design characteristics.
      My opinion is that this is indeed a very good and reliable design. Very simple. I think the real issue is whether the design (impingement, rod, or ???) is executed well. In the case of the AR-15, it is executed very well.

  31. The writer’s use of an 18 wheeler vs car makes no sense and actually hurts his argument. The 18 wheeler needs those wheels to handle the heavy load it is carrying. Can a minivan haul 40k lbs on four tires? Nope.

  32. What can I say that hasn’t been already said. In Nam I hated the M-16 but my gripe was two fold one was the ammo, I have never condoned the use of 22 caliber anything in combat, In Nam I switched to a Thompson that the Navy built me (on my dime, back then special pps guys could carry anything the military could get you ammo for but you paid for the weapon) the thompson lacked range and was heavier but it shot the same ammo as my 1911 so I could carry a lot of ammo, and it never failed to drop the enemy. In Angola Africa I carried the m-14 and it was a manstopper, but the guys with m-16s were wanting to trade for somthing bigger after the first week or so. again due to ineffective ammo. Now I know many of you younger guys feel diferent but I osually worked alone in the jungles of the world and having a round that takes one or two rounds to put down a target beats using six or more anytime. If I had Angola to fight over again where the most common enemy was 7ft tall and 450lbs I would want a gas operated weapon simaler to a thompson with a 16 in barrel and 50 AE fodder, or a piston operated AR in 458 SOCOM. Basically fewwer round with more effect. and yes I have built several DI ARs my favorite in in 6.5 Grendel and I have built an AR-10T in 300 WSM a great long range rifle if I do say so myself. My next build will be a piston operated AR-15 in 458 SOCOM with a 20 in. Barrel. so now you have the opinion of an old fart with way too much combat experiance.

  33. Great read that backs my position up in an ongoing disagreement with a good friend of mine that touts the reliability of piston operated over direct impingement rifles.

  34. I have been shooting 3 gun matches with a Del-ton upper on a couple different lowers for about 10 years without a hitch. I have changed the fireing pin once. Same barrel, same BCG. Thousands of rounds down range and it’s still going. DI is super reliable and very affordable way to go. Lube it well, feed it well and clean it once in a while. That’s all it needs.

  35. Yeah, the article is right that there’s more to the system than just putting an op-rod in.

    But the article seems to treat this as some intractable problem. I wouldn’t try and build one myself but it’s not as if the engineers at H&K or LWRC just shoved an op-rod in a DI gun.

    I know it seems to be an (oddly to me) love/hate kind of thing. If I could afford a nice expensive piston I’d love to have one. But I have no problem with DI either. Just different systems with different advantages and disadvantages. Much of the ones listed here seem mitigated or solved by engineering…if you can pay for it.

  36. I have taken several versions of the M16 into battle, and without fail they get fouled and then malfunction. I do not mean because it was not cleaned for weeks, it happened more than once in just one day! In contrast to the M16’s, our M14’s went on the same missions, even multiple missions without cleaning. We had no stoppages, jams, or other M16 like behavior, they just worked everytime, all the time. We had no failures with M16 variants that had been upgraded to a piston design, it simply works better.
    Bottom line, any firearm that puts fouling directly into the bolt has problems.

  37. Just my two cents…….I have 5 DI…… ARs two of which purchased from “CTD”….one from RRA……..one from “Radical Firearms and one from….PSA. All sorts of calibers……223 Wilde…… 5.56 ……300 AAC and .458 SOCOM. Kept properly cleaned and lubed ……No failures of any kind in over 1500 rounds through each. I do however use quality brass cased ammo and shy away from reloads, steel case and/or any hand loaded ammo.

  38. Friend of mine built a piston AR for competition, and he discovered that you need a different gas block for a piston gun. The gas block was getting pushed forward on the barrel by the pressure, and that was causing reliability issues that he’d never seen with his DI guns. Needed more bolts holding the gas block tight to keep it from sliding forward.

  39. Having trained with both the M14 and the M16 and having the opportunity to work with various NATO partner weapons, I’ll stick with my current choices. I have an HK91 and an HK93. They are not DI or gas piston operated weapons. They use what is called a delayed roller locked action. The chamber has flutes in it to ease extraction and yes they do get dirty but they DO NOT jam, FTF, FTE or any other problems the other types have. I feed them both cheap Russian ammo and some good stuff. The accuracy suffers with the cheap stuff but that’s to be expected.

  40. Although the author scratches the surface, he fails to adequately outline a lot of aspects to this continuing debate.

    1). A big misconception was that “piston driven” (or direct piston) solutions were born from a reliability standpoint. While the debate rages about which is more reliable, the reality is that for MOST applications and environments, DI systems are acceptably reliable. Under harsher conditions, piston systems have shown increasing reliability, However, the extent and relative benefits are at best, debateable. This is where the old guard claims PD systems are “a solution to a problem that doesn’t exist.”

    The reality is most of the need for PD originates from the DI’s limitation and flexibility with respect to barrel length and suppressors. The author begins to cover this aspect, but brushes the issue off as if it’s a trivial “set it up that way” affair. With the adjustable gas blocks of PD systems, not only does it satisfy the issues with short gas systems (which are very finicky and nearly have to be tuned to a single ammunition selection, if even solvable with reliability requirements applied). Even if you concede that DI can be massaged to pigeon hole a particular setup to work, PD systems shine in their flexibility with firing either suppressed OR unsuppressed, with a multitude of ammunition (sub or super sonic, heavy or light, etc). In summary, can a DI gun be made to run short and quiet? Maybe (not always depending on certain inputs). Can it be made to run short and quiet or loud with a wide range of ammo and still achieve exacting reliability? No.

    2. The author doesn’t identify the other valuable feature of PD systems which is cleaning. Anyone who’s ever served in the military and knows how to properly clean a DI rifle (and how it SHOULD be cleaned) will tell you it’s not a quick or pleasant affair. Cleaning a PD rifle is not only a breeze by comparison, it’s required much less to still function to a high reliability requirement. This aspect alone is worth the other “drawbacks”

    3. Lastly, anyone who’s been around more than a day will tell you that with ANY advancement in firearms, comes the “old guy” resistance to change. When the 240B was fielded, every crusty E7 turned their nose and swore the M60 couldn’t be beaten. 20 years ago, polymer framed, striker fired, Double Action only semi auto pistols found a LOT of resistance. Today they’re the standard. The reasons are similar across time and platform changes. “Parts availability” “familiarity” “commonality and availability” “cost” (most new weapon developments are expensive until further adoption by the market, competing firms etc). “Don’t fix what ain’t broken” is the cry of the short sighted. If not for engineers and designers who push the envelope, early advancements would die a swift death from the old crusties that refuse to jump ship until the other boat is already full of people.

  41. This article is extremely biased and kinda laughable. I’ve fired your run of the mill m4 will in service thousands of round put through them. Since being out of service I own both a BCM DI rifle and an LWRC piston driven rifle. Yes, the BCM is lighter but coming in at around 6.2 lbs naked BUT I have magpul furniture and a 14.5 in pencil barrel to reduce weight. My LWRC comes in at 7.2 pounds. Yes it’s heavier but has a heavy barrel and a VLTOR EMOD stock which ads weight and balances the rifle. While both rifles are great and reliable the piston driven AR is inherently more reliable in HARD USE and long periods of time where it cannot be cleaned or lubed because of the hot carbon gases being dumped on the BCG. If your an operator in the US military or a contractor overseas then the piston system lends it’s self more to those guys but for plinking, range days and training it’s not a necessity. While I would trust my life to both systems, granted they were built with quality parts and by quality manufactures/gun smiths, If I had a choice I would choose the piston system based on my experiences with both.

  42. Like any design, Eugene Stoners direct impingement gas system design for the AR15/M16 is a series of brilliant trade offs. I will just talk about a couple. Although now retired, in my past life I was a Design, Stress and a Reliability, Maintainability, and Supportability Engineer for the Lockheed SkunkWorks. I am also a Combat Vet and a shooter so I have had the ability in my career as a senior staff engineer to look and evaluate both sides of the design/user discussion. I am also a Gunsmith and a Master Machinist. The most obvious trade off on the Stoner design was locating the gas cylinder inside the receiver proper of the weapon, the major trade off is thermal load distribution vs exhausting potentially dirty action gases inside the weapon. The primary benefit of thermal load distribution is a generally increased accuracy ignoring all other actors, the dirty action gases can be minimized by selection of propellant and initially that was done although a damp operational environment was not a consideration. Had I been on the program as a reliability and maintainability engineer and a combat vet that would have been one of my concerns. The pressure developed within the gas cylinder that is inside the bolt/bolt carrier is 100% axial with no carrier tipping. The issue you discuss concerning the pressure of the propellant gases keeping the bolt forward by acting on the “rings” does not work the way you describe. In order for that to work the force acting on the bolt internals would have to be more than the force acting on the base of the cartridge, I have no clue at this point the surface area within the bolt to make the calculation, but I can definitely predict what the bolt thrust will be on the bolt provided by the base of the cartridge. A 5.56 Mil Spec chamber pressure of 61kpsi times the circular area of the base of the cartridge .0865″ circular area = 5280.75 lbs of force on the bolt face. Adherence of brass to the chamber wall reduces felt bolt thrust to ~about 30% of the total force BUT that is only in a dry chamber, an oily chamber can increase the bolt thrust to 100% something that no designer expects to see repeatedly unless they have designed the action around a lubricated cartridge in which case everything is made stronger and beefer. One thing to remember for ANY mechanical device is that all stress is accumulative and once the elastic limit of a metal is exceeded it does not relax back to normal.

  43. Since ~1960 the military has tested the M16 based rifles and carbines in every configuration. Here we are 55 years later, and the DI rifles continue in service. If the rifle failed like the first AR15-M16 they would fix it. Wow, the Army did fix it with the M16A1. Then the troops asked for a heavier rifle and better sights, and the army delivered the M16A2, still using DI. Then Colt gave the army M4 carbines with improvements Colt felt gave an improved system. The M4 carbine became standard issue. The Marines hung onto the A2, but is now transitioning to an M4 PIP. If they did not work, and outperformed piston rifles, then I’d say the GIs have a damn good weapon.

  44. I have found that plating the bolt, carrier and related parts with NP3 makes a rifle every bit as reliable as an op-rod rifle. The high lubricity of the nickel-Teflon keeps the rifle functioning when dirty. Because of reduced friction, the bolt stays cooler and lasts longer and clean up is as simple as wiping the parts with a rag so the rifle can get back to what it does best. Back when I was at Tactek Arms, I built a custom .300 Blackout rifle for a customer in Memphis. He uses it to hunt and protect his family.

  45. 2 K rounds through my SR556 & the only problem I have is running out of ammo, oh and I haven’t cleaned it yet either.

  46. I work for Layke Tactical and have manufactured a little over 2000 LT15 (AR15) DI guns. We have guns being used by local shooting ranges for rental with 30,000 plus rounds with no failures. In my opinion the piston system eliminates a problem that does not exist and creates some of it’s own. I have owned and been building DI guns since 1977 and have never had a DI system foul, I clean my guns after ever shooting session whether I fired it once or a 1000 rounds. We have built a number of piston guns for customers that insist on one, the piston gun will foul or fail at the piston and is more likely because piston owners think they have a gun that does not need to be cleaned. So why complicate a gun and fix a problem that is not. A firearm is like a car or any other mechanical device, keep it cleaned,lubed and maintained and it will last a life time.

    1. As a side note to my comment, the only mod I would recommend to DI gun would be a adjustable gas block so you can reduce the gas needed to operate to a minimun. There are few manfacturers out there but I prefer the ODIN adjustable gas block.
      P.S. I have no connection to ODIN

  47. “If you still think of a standard AR-15 as inherently unreliable, you need to get with the times.”

    I do? Prove it. What major change in the DI system has occured in the market in the last few years to make me so “behind the times” by believing what I have seen with my own eyes. I, and many of my friends, were consistently let down by our service rifles in a combat zone thanks to the design flaws behind the DI design. It’s extremely dirty, dry, and hot as heck. This is a horrible combination in extreme climates. Weapons like the AK didn’t get a powerful reputation for reliability over the AR for no reason, and you just asking the reader to throw out years and years of hard learned lessons is insane.

  48. I am enjoying this conversation because I am currently building my second AR with a gas piston kit. The first one is an Anderson Mfg. lower on which I installed a Geissele SD3G trigger and a 5.56 DI upper from M1S with an HCAR barrel. The barrel came with a FSB so I only had one choice for a gas piston kit. It is the OPS-416 from Osprey Defense. The piston kit is very low curving around the barrel so I can continue using the free float forend I had. This rifle worked perfectly after about a 30 minute install. I like it better than the DI because it is cleaner but just because (in my mind) it feels crisper. So that is my first one and I like it better than when it was a DI. Now the second one is a different story. It is/was a DI AR-15 (also on an Anderson Mfg. lower and Geissele) but with 7.62X39 upper, ER Shaw 16″ HCAR and DPMS receiver. It also had a FSB which I am partial to. Problems to start with: OPS-416… under gassed and FTFs. Bored out the gas port incrementally to 1/8 inch no help. shortened the buffer spring no help. tried different mags no help. Polished feed ramps no help. So, I finally gave up on the AR-15 upper and opted for M4 upper receiver and M4 barrel insert. Now this 7.62X39 works as well as the 5.56 and I am happy. Unfortunately, there is not enough information on the web or elsewhere to indicate the upper receiver and barrel insert should be M4 for the ramps to accommodate the gas lower gas pressure and miscellaneous mechanical feed problems. However, it does work so anyone wanting to put a kit together with this caliber can take this under consideration. I don’t have a factory GPAR but my nephew (major in the Army) does and he loves it. I have an AK-47, an SKS, an SVT-40 and an M1A which also are all piston guns and I like (no… love) them too. This is all my own preference because the DIs are proven and work every bit as well when kept clean. I guess my introduction to military rifles was the M14 used in my time early in Vietnam, hence I am a gas piston fan.

    1. FYI the failures to extract I’ve seen were caused by poorly machined chambers characterized by concentric tool marks, I.e., “rldges”. A 410 bore mop with metal polish on an electric drill for 30 seconds can eliminate the problem.

  49. Having put high volume auto fire through a DI system, 10’s of 1,000’s of rounds easily-I never had an issue. If it gets to hot, it’ll cook of the entire mag when you close the bolt. High quality ammo has never caused an issue. Cheap Russian crap is an issue-on most any quality firearm. If your running a can, get an adjustable gas block-too much blowback on a DI. Di has to much movement, less accurate. I’ve trusted my life to DI, and it never failed me. Had a Plt Sgt shoot through a mud plugged barrel, no issues-other guy, issues. The DI has been in every environment on earth, and it works, keeping grunts alive to fight another day. There have been more piston driven rifles dropped from dead hands than DI rifles.

  50. I learned many years ago the substantial advantage of a piston system over the DI system when I owned both an AR-180 and a slick side Colt AR-15 (M16A1). The piston AR-180 ran flawlessly despite being a cheaply made steel stamped piece of overly heavy junk. The elegant Colt was good for maybe 100 rounds before it started having problems. It had to be run wet, cleaned with a carbon pick, and the lower required regular flushing of carbon and grit and re-lubrication.

    These days I run an Adams Arms piston upper and it has zero malfunctions in 3000 rounds, stays clean, and runs almost dry. It about 6 oz heavier than a comparable DI upper would be and it’s worth that extra weight in gold.

    Did I mention it shoots about 1/2 MOA with Hornady Superformance 75 gr? So do the 2 Adams Arms piston uppers my boys have.

    No more DI ever for me,I’m a piston AR guy forever.

  51. Come on guys, get your story strait! Just last week you listed the “best ARs” with multiple piston based models and number 1 (best) being a piston operated system. Now you publish an article that basically states that piston/rod operated ARs are crap? Flip flop much? How bout next week? An article why you should never carry concealed?

    1. Its just a pathetic sensationalist article to try to get page views and stir up people to comment, and maybe drive some sales.

      Very weak stuff.

    2. If you read the article again, it states that the op rod system is better if MADE correctly and don’t mind the extra cost & weight. . “Granted, many companies (such as LWRC) have perfected the overall system and removed most of the early problems. However, this comes at an added cost.”
      FYI- I have shot uncountable rounds of ammunition for many years in my military issue gas op rifle. Served as a squad leader during multiple deployments, I trusted my equipment with my life. Also being a range safety NCO at another duty station has its perks to shoot until you get bored each day.
      I NEVER HAD ANY PROBLEMS!

  52. I have the lwrc and several gas impingement rifles. I shoot lots of wolf steel ammo. The lwrc never really needs to be cleaned but the gas gu s do after every use or the bolt and carrier can get seized in there.

  53. I’ve got a CMMG piston upper that I run FA on a registered lower. When I was running a DI upper on it, I had failures occur from broken springs that quit from the heat. I also had an issue (fixed with non-rotating pins) where carbon grit was causing accellerated wear in the pin holes. And exactly one time I had a gas tube crack. I clean my firearms inside and out after every range trip – so none of those issues were cleaning related.

    Since I went with the piston I have had zero failures. The weapon runs cooler and cleaner. I use an enidine buffer so I don’t notice any discernable difference in the ‘feel’ of the battering the weapon takes during firing – but after several thousand rounds I have noticed no abnormal wear in the upper receiver or BCG. After it initially ‘took a seat’, it has run happily ever after.

    Now, some have spoken about gas pressurising being essential for proper function. Well, I’m no scientist – but I do know that the upper to lower seal is anything but airtight on the best of days, so I personally don’t see any issue with the loss of any pressurisation which occurs using DI. The sole exception to that would be that I no longer have anywhere near as much crud to pick out of odd corners and pin holes as I once did.

    Others have spoken of an off-center force being applied to the BCG by the piston. I personally believe that is also a non-issue. Again, I am not a scientist – but given that the part which receives the operating force in both systems is staked above the plane of the BCG’s travel, both systems by definition are delivering off axis force. I don’t see any substantial difference in the amount of force received in each system as the shock front of expanding gas and the face of the op rod both travel the same distance from their entry points to contact their target on the bolt carrier. I wouldn’t want to put my finger in front of either one and pull the trigger! The point being, the ‘hammering’ the BCG experiences is about the same in either system. So again it makes little if any difference.

    Unless you prefer a cleaner and cooler running rifle with zero heat and fouling induced failures. I was sceptical at first – but after running one myself I am a piston believer. Sure, they say if it ain’t broke don’t fix it. Well, from what I have seen, DI was broke by design in several ways that the piston has fixed.

    That’s my two cents.

    1. The DI guns don’t have an off axis force being applied. When the gas enters the bolt carrier is directed into the carrier (cylinder) and shoves equally against the bolt (piston) so the carrier gets directed rearward uniformly and not off axis. The gas hitting the tube atop the carrier is not what drives it. In the French MAS 49/56 the gasses hit the cup on the carrier and that does drive it rearward.

  54. I have built both DI and piston AR systems, and the reliability of each depends on the manufacturer and/or the one who assembled it, as well as the user. I don’t believe the author has any direct knowledge of a piston system, but is just passing on regurgitated internet BS. The photos he added were of a BCM carrier, so evidently he has a BCM gun, which is one of the most reliable in the business, and one of the more expensive guns. By the way, the brand names of AR’s he dropped were the more expensive brands of DI guns. I noticed he didn’t mention the lower cost guns like DPMS in the group. There are piston systems available, such as Adams Arms, that add about an ounce to the weight of the firearm, which unless you are rucking up the mountains of Afghanistan or some such activity, you probably will not notice the difference in weight. If you are building the upper assembly from a stripped barrel, the cost difference will probably be only about $50 bucks or so, as the bolt carrier, gas block, and hand guards are included in the kit. If you have a DI AR, and you like it, good for you. Some of the advantages the author conveniently didn’t address. If you are buying the Russian steel jacket ammo in bulk to save money, the piston AR’s have a lot fewer malfunction issues with the steel case ammo. Depending on which system, they are usually easier to clean as well. If you have a bumpfire stock, the piston AR’s have more felt recoil, which makes the stocks work better. I am sure there are others who found more BS with this guys post than I did.

  55. I too have military experience with the Gas tube (DI) M16. I have had zero issues with a well maintained DI M16. I also have civilian models as well with no issues. I did get caught up in the hype surrounding the piston conversion for a time and was considering a change. However, like someone before mentioned “it was an answer to a question I never asked.” I am not saying I am against piston systems (my AK has one and works quite well!) What I am saying is with proper and regular maintenance I have had zero issues. Someone also mentioned “clean it like your life depends on it” truer words have not been spoken.

  56. The article should have been named: 4 “Opinions” Why the Operating Rod AR-15 Might be the Worst Gun Idea Ever.

    The article was full of the chock full of opinion and sorely short on facts.

  57. Slightly off topic. But an AR with a short stroke piston is no longer an AR. I’m sure most know an AK uses a long stroke so this mis understanding that your adding AK reliability to an AR by add a short stroke is false. Simplistic I know but your making more of an SKS. If you go the whole Op rod route why not get a firearm designed from the start, with a folding stock?

  58. Explain to me again why you don’t heat your car by direct engine exhaust ! You could eliminate the fan that might break down , the heater core that might leak , and the stereo system you could not hear ! Stand the author of this article in the corner for wasting space on a non-issue !

  59. The author seems to not understand physics. With a DGIS rifle, yes, the bolt is pushed forward once the projectile passes the gas port, with the exact same force as the bolt carrier is being pushed in the opposite direction. The length of the barrel forward of the gas port is critical to extraction. The internal pressure causing the case to “lock” to the chamber is the same in both systems and an “ideal” length of barrel in front of the gas port if 7.5″ allows the pressure to drop in both systems for proper extraction. If his statements were “true” based on science, would not most of the piston systems be ripping the rims off of cases?
    I have shot next to individuals with high dollar “high quality” DGIS guns that were blowing primers out if the cases. When I shot the same ammo they were using from thier mags to see what was happening in my piston rifle I had completely different results. If what the author claims is true I should have had even worse results instead I had clean consistent extraction, primers still the cases, just like normal. The ammo was blamed and I was happy to be given this “cheap Chinese crap” because they wouldn’t shoot it any more.
    People seem to forget that an AR is not a “true” DGIS rifle. The original DGIS simply tapped pressure from a port in the barrel and “blew” it onto the bolt carrier forcing the carrier to the rear which in turn unlocked the bolt and started the extraction/ejection cycle. (See ENT 1902, MAS 49/56). Stoners design routes this pressure into the carrier and uses the bolt itself as the piston, so in effect all AR’s are piston systems. Look it up, even Stoner said that his design was not DGIS. Author needs to do more research and less B’sing.
    I would like to see some testing comparing timing between conventional op rod systems and Stoners design as used on AR’s.

    1. Could not edit to correct my error.
      Should read ENT 1901 (Rossignol ENT).
      Big thumbs, small phone.

  60. This artical lost me before it got started when it said “A semi-truck has 18 wheels designed to drive long distances. Wouldn’t it be awesome if your commuter car did too?”

    It has always been my understanding that distributing cargo “weight” is the main reason for “18-wheelers” having lots of wheels. With heavier loads having more axles and thus wheels to distrubute that weight across the road surface for which design capacities regulate.

  61. I have two op rod rifles, a M1A Loaded, and a tactically configured Mini 30 chambered in 7.62×39.
    One DI AR (Sig 516), two gas tube AR’s, a Colt (Accurized A3) and a Bushmaster Varminiter
    The bottom line is that they work very well, never a single issue from any of the above and I know if I were ever to have issues, replacement parts are a mouse click away.
    I’m from the school of thought that “if it ain’t broke, don’t fix it.” At the same time clean it like your life depends on it because someday, when it’s least expected, it just might.

  62. Here is my objective testing- I like shooting both GI and PD in 5.56 and 7.62. My only complaint is the staining of the brass in my suppressed 5.56 and 7.62 GI rifles. My rifles function flawlessly as long as I keep them clean.

  63. @Retired75th, let’s just say the most effective thing.
    Since Obama took office, firearms sales have soared, intelligence and mind be damned.

    This very gun blog has repeatedly championed “Obama Gun Grab” bull crap, idiot follow.

    The Obama Gun Grab is *so* 2008. Reality shows that Obama is a wussy.
    Well, repeatedly shown.
    The reality continues, we have a Constitution.

  64. @Schmairb Dandlefatch, the author seems to be against retrofitted piston systems, are any of yours retrofitted or original piston systems?

    Ideally, objective testing should be performed to ascertain if the author’s stated problems actually exist or if this is just an opinion from a jaundiced perspective.

    1. The author has apparently NOT had military experience with the M16/AR 15 series of rifles…Yes, proper maintenance will keep ’em running under fairly low maintenance/firing ratios, but in any kind of extended range session /firefight the AR will get dirty ad will quit.
      There was a reason why the SOCOM folks had HK look into the issue to begin with.

    2. I cannot discuss that, due to an NDA.
      Which royally pisses me off, but the NDA wins for good reason.

    3. Spent a year in Vietnam, was in Firefights 3 or 6 days a week, kept my M-16 clean inside and out, never had a problem. When my year was over and I turned in my rifle, the weapons clerk asked how long I had the rifle. I told him a year and he told me that they recalled all aluminum bolt actions about 6 months ago. The key is to keep it clean and well lubed. There were guys in my platoon that thought wiping the outside with oil was clean enough, they were the ones trying to un-jam there rifle in the middle of a firefight.

    4. “…the weapons clerk asked how long I had the rifle. I told him a year and he told me that they recalled all aluminum bolt actions about 6 months ago.”

      What-huh? Aluminum bolt actions? Are you serious?

  65. All those reasons SOUND ok….but then I look at the Garand/M14/M1a and AK series…and they lose half of any weight they had. two of the most reliable battle rifle systems around. Period.

  66. Wow. Really disappointed CTD ran such a bias and arguably significantly misleading with MANY half-truths.

    I would have had much more respect for CTD if they chose to run a “pro-piston” or ambivalent perspective parallel with this “article”.

    I own both styles of AR in multiple calibres. I have had ZERO issues the author claims piston configured weapons are “plagued” with.

  67. really? this means you will make more money if someone buys YOUR product. if you think gas impingement is as good as gas piston ,,you make morons look like geniuses. sierra tango foxtrot uniform!

  68. As former Law Enforcement Official, plenty of time and Thousands of rounds through my duty weapon I can honestly say that my gas (old-style) system performed well with not one issue. I have since purchased various brands such as Rock River,Bush Master,Windham Weaponry, and M&P which I will say They all perform well to this day.
    Ill stick to the Original design,not saying piston is bad, just my experience has not failed me yet.
    Keep shooting and enjoy your weapon.

  69. I’ve been shooting and working on guns my whole life, so I decided to get my gunsmithing degree,,, while I consider myself a an armorer and not a smith that’s not what my diploma sez. I have shot and built more AR’s then I can count, taught people how to care for and shoot them and had very few problems with a DI system. I’m not gonna work on something that works well.

  70. I’ve had extensive experience with ARs for over 30 years, and feel that adding a piston assembly is the answer to a question I never asked. It seems to add complication and weight for dubious advantages.

    I’ve heard the stories of the early days when the M16 was introduced in Vietnam, but that has not been my experience with the M16A1, -A2, -A4 or the various civilian and law enforcement weapons I’ve been issued, carried and/or owned.

    Yeah, the AR is tricky to detail-clean, but field maintenance takes a jiify. It does need daily attention, and proper lubrication.

    On the plus side, it is ergonomic, light, fast and accurate.

    The AR-18 used a piston, but I never had one of those.

  71. Hey! Today is my birthday (66) still a young pup, but I can’t unserstand spending my time here reading this stuff. I guess I’ve lost that time management thing. Yes I do shoot as well, lots.
    Semper Fi and Go Army! You guys get along now, ye hear?!

  72. I to had my switch flipped!! I have always understood the importance of the second amendment but wasn’t a big gun fan until our right came under attack from this administration. The switch was flipped In a big way!!! I can’t get enough gun stuff now!! Absolutely love the sport, the friends, the challenge, the beers afterwards, etc, etc.

  73. I had a strange issue awhile back. My AR would either 3/4 cycle and fail to reload next round completely or it would “short stroke” and fire full auto at a very fast rate. After much discussion, many hours of inspection and thought I finally noticed blacking or carbon build up on the gas tube right at the gas block. Someone had put the DIRECTIONAL ROLL PIN in backwards and slightly off this elongation of the hole. This caused just enough of a gas leak to totally mess the function of the rifle up, COMPLETELY!!!
    Literally, a roll pin and new gas tube correctly installed fixed the whole issue. Haven’t had a malfunction since!!!! Hope this helps somebody so you don’t have to pull your hair out like I did for way to long. I’ll chalk it up to being a newer AR guy!!!

  74. Aside from the blatant sales pitch for the mostly high-dollar companies mentioned in the article … the writer is a buffoon, misleading, dishonest, and almost entirely wrong (with the exception of piston systems being SLIGHTLY heavier). Worthless article.

    1. Here here!

      Surprised CTD hasn’t pulled this “article” down yet as it reflects poorly on them.

  75. Very good article and a few very good comments. However, carrier tilt wear alone is insignificant and other major components will wear out first. I have a few quick comments re piston guns. Author touched on the fact that each manufacturer has their own proprietary design. Twice in the last 15 months an AR with a conversion kit has come into the shop and parts needed replacement. Both companies still in business. One no longer had parts. One did have replacement parts, but they did not fit. Owners had 3 options – go back to a DI system, replace the entire kit or have parts manuf. One went back to DI, and the other replaced the entire upper with a new op rod system while the old upper I converted back to DI. He did a lot of 3-gun. Have to remember the company you buy your upper or kit from today may be out of business in 3 or 5 years and you may not be able to get replacement parts. In a SHTF scenario, and everyone should think in those terms, you are SOL if you need piston gun parts that will fit your system. On the other hand, there will be DI AR parts available for quite some time to come even after production has stopped. Small or family run piston gun makers that have and will do well while Obama is in office, may later on have a harder time competing with the major manufacturers and some may fold up. So be careful where you get your kit or upper from, if you decide to go that route. The other comment had to do with wear. We get a few piston guns in each month. Due to the design, critical parts seem to wear more quickly than (I believe) they should depending on manufacturer. Author summarized them so I won’t repeat. I think this is an important consideration if you are undecided. Another thing, the op rod sits well above the bore centerline, that, plus the dynamic reciprocating action can affect full auto or followup shot accuracy. If you try to compensate with a stronger buffer spring or heavier buffer, you might get short cycling. Lastly, I have been told by customers that some ammo can affect piston gun function like short cycling and combine that with a SBR, you might need to be more selective with some ammo. A gas valve in the gas block might correct that. I strongly agree with one commenter that SBR’s with or w/o suppressor make the best use of op rod system. On a carbine or rifle, I personally see more upside with a DI system. I agree a cooler running weapon is a significant advantage, and easy cleanup is important as well. But there are one too many negatives (IMO) with a op rod system. Regarding cleanup if you haven’t tried already, get some of the more advanced cleaner/lubes that actually penetrate the metal and provide some additional lubricity, and really do make maintenance quicker and easier. We been at war now for some 14 yrs, if the AR with DI was so outdated, problematic, prone to malfunction, and so hated by the troops…we would have heard about it long ago. The basic AR platform with DI is here to stay for a long time. Otherwise you would not see such a HUGE ongoing investment in the AR by the govt and the gunmakers. You see gunmakers FINALLY focusing on additional calibers and accessories. My major gripe with the AR since 1965 in Vietnam has been and always will be the caliber, not DI, which is an excellent system. Invest in good quality pipe cleaners to clean the gas tube / block.
    One last comment re bad rep AR’s have. One of the biggest reasons why the first AR’s in Vietnam fouled so much and M16s got such a bad rep had to do with the propellant (gunpowder) – STICK versus BALL powder. The gunpowder used during the military trials was relatively clean burning and not the same powder used once the weapon was issued to the troops. Hence the significant fouling.

    1. @Retired75th. Concerning the early problems with the AR in Vietnam, you are exactly right. Most of the problems were caused by the propellant being very dirty and fouling the barrel, gas system and bolt/carrier with heavy use. Cleaning and lubricating in the field was an everyday requirement to keep the gun operating properly. When the problem was recognized, the propellant was changed and the gun preformed very well. Lubrication and cleaning remain very important to keep wear to a minimum and parts life at maximum. I have two DI guns that perform flawlessly.

  76. Of course I quit making gun purchases based on need sometime back. I want a piston rifle I saw at the range one day that was a piston rifle and my wife said I like his better than my colt. Now that is a need for another AR if I ever heard one.
    Second reason is I want to start out with two sparkly clean rifles that will then have the snot hammered out of them with good ammo, match ammo and the nastiest crap ammo I can find. I want to know what chokes when before my wife has cause to use it to protect her and our dogs from coyotes, feral dogs and feral hogs which all pose a great danger to us and our dogs. We are also seeing diesesed deer that are a danger. I believe in being thorough , how thorough, when she decided on a Springfield 9mm XM as her new carry gun I fired five thousand rounds of all manner of ball ammo prior to firing a thousand rounds of her choice of carry ammo. Until the last round of carry ammo killed the last piece of rabid fruit I did nothing. I did not clean, lubricate, or do anything except load magazines. I would take those pistols anywhere with no thought.
    Which brings us back to ARs. I shoot service rifle with Garands and M1a ‘s in the eighties. Twenty two caliber anything was a temperamental mouse gun. I started shooting service rifle again back around two thousand five with my son who was given a national match AR by a friend. I knew nothing about its strengths or weaknesses. So I built a few rifles for friends and relitives. I’ve never had a problem with any of them and that’s saying something since the knock around rifles went on many a CAMPOUT with fathers and sons with all manner of clay birds for targets and factory ammo. We started with clean rifles and we used reprints of the cartoon book to clean the rifles in the evening. In the morning we got up, did morning details and started over. My daughter certified in the Air Force with the AR and asked for a quart bottle of break free.
    In closing yes I need a piston driven AR.

  77. I’m glad they did this article. Not that it was so great, but I appreciate all the comments. I’m new to AR’s. I’ve had an Adams Arms for a little over a year now, and have no experience with a DI AR rifle. I can say that I’m happy with my AA. The only problem I thought I had was in cleaning it. Whenever I cleaned it, It took me forever trying to get it clean. It looked clean, but my rags and patches never had much dirt on them. I finally realized that the rifle just didn’t get very dirty.

    1. The writer is pushing gas impinged systems and fails to mention that before a rod gets pushed the same gas pressure building that makes the direct impinged system less ‘abrupt and violent’ is also at work, only further up stream, away from the bolt. This lack of honesty is unacceptable.

      BER

  78. Have had an LWRCI M6A2 gas piston AR .556 cal. for over 5 yrs now , never ever one single problem , no wear inside receiver at all , around 2 or 3 thousand rnds so far ! Got a gas impingement Bushmaster I’ve had for about 15 yrs , probably same rnd count , no problem with it either , I run wet with very good lube though ! 😉

    1. While in the Army, the standard rule was don’t lube the rifle. When I instructed soldiers I always told them to lube them. We used Break Free, and it worked well. My lessons were to clean and lube them, but get as much EXCESS off. Always leave enough to prevent rust, but not enough to congeal. They worked very well. If you have an air compressor, blow off and out the excess oil. That very thin lube works on ARs or AKs.

  79. “Properly built guns, such as anything from Bravo Company Manufacturing, Daniel Defense or FNH, USA will be as reliable as the day is long.”

    “…and shoot the snot out of it with quality ammo.”

    Yeah, see, I don’t want to spend my time and money building the “perfect” AR, or feed it quality (Read: Expensive) ammo. I don’t want to carefully and lovingly clean every last millimeter of my gun’s interior every time I touch it. I want to pick up a gun for under $600, shoot it cheaply, and not fret if I don’t clean it thoroughly every time I shoot a mag through it.

    So… I went with a piston gun, the ever popular AK, a Wasr-10. Accuracy is a big fat “Meh” with cheap ammo, but it doesn’t fail me or need to be babied.

    Only problems I’ve ever had have been with badly dented surplus mags that hung up the follower and didn’t feed rounds, and one time I tried to feed a winter glove through the action when cocking it and it didn’t like that. (I never liked the stupid cocking with your pinkie anyway, so I stopped doing it anyhow. Doesn’t make much sense to cock with your weakest finger…)

    1. Sir, As a military armorer with close to 40 years direct experience working with the AR system, I realize that the ARs are far from perfect, and must be meticulously maintained. Having said that, because I know how, and have taught God only knows how many people to operate and maintain their weapons, I can say that I prefer the Ar over anything else available. Yes, the AK shoots when dirty, and is not finicky about the ammo you put in it. Yes, the AK is completely reliable. But, even with the best ammo, it has severe limitations as to accuracy. An AR can be maintained to the level of absolute reliability, it just takes a little more effort, time well spent in maintenance, no matter what you are shooting! I only have experience firing military ammo, and my personal reloads, but, I would put my AR up against an Ak in any scenario I am willing to be involved in. Yep, the AR is not perfect, but, it works for me…and millions of US troops, as well as our allies. You can’t argue with success, my friend…

    2. Oh, right, the discussion was Op Rod vs Direct Impingement… Sorry, I am accostomed to defending the AR, just on general principles. So, why go away from the DI system, and embrace the Op Rod? Because it is better, that’s why! Yes, there are a lot of hand built guns out there that run great with the Op Rod, but, if you do your maintenance, you don’t need the added expense, and weight, of an Op Rod system, especially since the gun was originally designed my people who are light years ahead of most of us, and I think they did it correctly, right out of the box. Had the government bean counters not gotten involved, we might have lost a few less guys in the RVN, and maybe so many US troops would have been better able to use the weapons they were given, instead of gleaning Soviet rifles off of the battlefield. Water under the bridge, but I still think about it. I am convinced that we are better armed with the AR…

    3. You can’t argue with success, my friend…

      Vietnam
      War in Afghanistan
      Iraq War

      We left with 72 men in our platoon and came back with 19, Believe it or not, you know what killed most of us? Our own rifle. Practically every one of our dead was found with his (M16) torn down next to him where he had been trying to fix it.
      — Marine Corps Rifleman, Vietnam.

    4. Well put, sir. I will take reliability over “quite accurate when you can get it to work” any time my life is on the line.

    5. That’s what happens when maintenance training, cleaning kits are omitted and the ammunition is substituted for a dirty burning powder that wasn’t specified for.
      One should never substitute a primary weapon in the middle of a war, it should be substituted in during training, then fielded.

      The M14 was resurrected and M1A’s purchased for the wars in Iraq and Afghanistan as a designated marksman rifle.
      I’m saving up my pennies to get one for myself, as well as that LE6920SOCOM. They’ll have to wait until our relocation if completed though.

    6. I’ll put my HK91 up against the AR platform any time. It is very accurate, it will shoot ANYTHING I feed it. Some real cheap (Tula) ammo is less accurate but that is the round not the weapon. Yes it is heavy but I’d rather pack the weight than have to spend hours maintaining it. I used it last year to drop an 8 pointer. One Shot One deer! I paced the distance at approx. 316 meters! The AR could NOT do that!

    7. Uggh! Not this argument again. Can’t people just give it a rest already with it boiling down to personal preference?

      I own both platforms so I’m not particularly biased. Both platforms have their advantages and weaknesses compared to the other, and both sides tend to exaggerate their POV.

      The AK accuracy *DEPENDING ON VARIANT* is not nearly as bad as you make it out to be. For example I can pull about 3 MOA out my MAK 90 with Wolf ammo. That’s more than enough accuracy to get consistent head shots or harvest a deer @ 100 yards.

      Likewise I know that the AR *DEPENDING ON BUILD QUALITY* is not nearly as delicate a rifle.as a few people have made it out to be either. However as the expression goes, you get what you pay for. The OP is right about one thing though, you’re not going to find a new AR for under $600 that is worth a damn

    8. Darn it! One of these days, I will learn to proof read what I write before I hit the submit button! What I meant to say, right off the bat in the second post was that I think the Direct Impingement system is better. Ok, I’m out! Peace…

    9. I spent 24 years in the US Army and trained with the M14 and M16. I DETEST the M16, it was a POS in my opinion. They have improved it but it is still not a weapon I prefer. I have a delayed roller lock HK91 that shoots anything I feed it and has never failed in over 10,000 rounds. It does get dirty but it will still function reliably. The M14 or M1A is still my favorite but can’t afford one YET!

    10. US Army retired, fought with M16, M4, M9, M1911 and M1A.
      Thankfully, they replaced that M9 with the M1911, even aiming to please the bastards didn’t always drop with a 9mm round.
      Failure to feed or fire was rare for any of our weapons, but when we weren’t on patrol, we were cleaning the weapons. That carbon encrustation on the back of the bolt was something I didn’t tolerate.

    11. My dislike for the M-16 stems from having to stack the bodies of dead men, on my tank to get them where we could load them on a helicopter, and they had their weapons torn down trying to FIX them. Simply put I DETEST the AR with a DI system. I fought with all the weapons you mentioned and I DETEST the M9 as well. I have my own 1911 that I shot in competition on active duty and it never failed me. My HK91 is not an American design but I got to shoot the military version (G3) while training with the Germans. It is VERY reliable, shoots anything you feed it and is accurate. One day I’ll have enough saved to buy an M1A.

    12. @US Army (retired):

      Your comment is more convincing than any others. Can you please tell me a couple/few makes of AR-15’s (preferably under $1000) that have the proper system that you approve of?

      I’m not an expert on AR-15’s and I honestly didn’t know they had all these unique differences. Any help or advice you could give me about specific makes would be appreciated. I trust you and thanks for your service!!

    13. ss1, The closest I can come to answering your question would be to consider the Ruger SR556, which is not under $1000. Another would be the Ruger mini-14 with the tactical stock. That would be under $1000.

      My current go to rifle is a civilian (HK91) 7.62 version of the German military rifle (G3) that was in service for 40+ years, It has a very different operating system in that it is a delayed roller locked system. I personally just prefer the larger round.

      A 5.56 version (HK93) of the same operating system can be had for under $1000. This version even has 40 rd mags. The ejection is very robust with either one. Another thing I like is they will shoot any kind (cheap or expensive) of ammo you put in them!

    14. @US Army (retired):

      Thanks for the advice!!

      First I want to clarify that I already own a DPMS LR-308 AR-10. This is their lower priced model, so I’m going to assume it’s the DI style that you don’t prefer. I also own 2 AK’s, and I’m a huge fan of that platform.

      But after seeing men on the shooting range with AR-15’s, shooting extremely rapidly without the muzzle lift that my rifles have, and also selected men with compact silencers that have extremely good noise reduction, I have decided to get back on the 5.56mm bandwagon.

      With the Ruger SR556 being out of my price range right now, I did research on the HK93 just now and found the C93 from Century Arms selling right here on CheaperThanDirt. I really like the look of the C93 (because I like AK’s anyway), and if you say that this style of 5.56 rifle is more reliable than the AR-15 platform, it’s going to be the next gun I buy (after I sell a couple I’ve been procrastinating on).

      If you have any critical comments on the C93, please let me know. But I couldn’t find an HK93 in my Google search.

  80. I have both DI and gas piston AR’s. The only reason I prefer the gas piston is that I don’t have carbon build-up in the bolt carrier group. The gas piston system stays relatively clean. The bolt face gets some primer residue and of course the bore collects residue. Very easy to keep clean.
    I’m a Viet Nam vet and served a total of 14 years in the Marines. I never had an M16 fail on me but I remember cursing the damn things many times when trying to keep them clean. No matter how much time you spend cleaning the bolt carrier, it’s almost impossible to remove all the carbon build-up from inside the carrier, especially in a field environment. The failures that I did see in the M16 were caused by clowns not cleaning their weapons.

  81. What I find disturbing about this article is that the points are not backed up by any thing that looks like the results of a study nor are there any stats.
    This tends to make me think that it is more emotional than factual.
    This appears more like counter sales energy to the suppositions supporting the use of piston systems.

    Just saying.

  82. .This is a non issue for me. I can appreciate what both systems have to offer . Gas Piston for low maintenance, and Direct Impingement for it`s light weight which no one mentioned. I plan on adding an AK-47 here soon. I am truly fascinated by the engineering and history behind each weapons system. I started as a casual gun owner and hobby into a passionate love for firearms. I never gave much thought about guns until I got Married and had a Son , then it seemed almost over night I started to feel a calling or want to be able to protect my family and home. It`s funny, it was like some one flicking a switch in me .

  83. Everyone seems to be overlooking a 3rd option. The recoil-operated rifle.
    Germany and other countries have found that the H&K G-3 and similar rifles serve them just fine. Of course the recoil on these, especially in
    7.62 NATO is brutal. I know, I have used these weapons. Like JD MAK, if I had to choose only one to go into harms way, it would be the AK-47. The AK- 74 is a good weapon, but I just prefer the larger caliber. All DI rifles that I have used and encountered, regardless of manufacture or generation, are tempermental and require gentler handling than do weapons that use an operating rod system. As in all things; however, this is my personal opinion and I choose what works for me. Others have differing opinions and choose what works for them. It comes down to what you like of what works best for you. Some like DI, some operating rod, and even some, ‘that enjoy pain, I suppose,’ (I don’t), prefer the recoil operated systems. For others, the only choice is a ‘turn-bolt.’

    1. The G3 isn’t recoil operated. It is roller delayed blowback. In normal blowback just the weight of the bolt carrier and recoil spring holds the bolt closed until pressure drops. The excess pressure pushes the case backwards which opens the bolt and ejects the round. More powerful cartridges would open the bolt too soon so the G3 uses rollers on the bolt which act on the carrier to force it back faster than the bolt which delays it just enough to be safe.

      The problem with this is, although very simple, is the speed at which the carrier moves. It is very fast and extraction occurs when pressures are still high. This results in higher felt recoil and hard extraction which can rip the rim off of a case or deform the brass. HK got around this by fluting the chamber so some gasses blow by the case. This releaves pressure and causes the case to float in the chamber easing extraction.

    2. Zach, that is the very reason I own an HK91 (civilian version) of the G3. I did have a muzzle brake installed by a gunsmith, it is similar to the one for an M14/M1A, and it was great in reducing the recoil and barrel rise to the point that I can make quick and accurate follow up shots. I have put over 10,000 rounds through without a single malfunction! The ejection is robust but I also installed a deflector on mine that allows me to reload my brass. No more dented cases!

    3. I have a Bushmaster Carbon 15, 1st model w no muzzle threads and w a 30 round mag it is featherweight, also have a DPMS AR 10 copy that is way to heavy with a 16″ barrel same heft as a RPK. I am looking to get rid of the DPMS and get a receiver for a metric FAL for .308. But the AR platform was designed for DGI and AK was a piston. 2 different animals. But in todays world you need something that will cycle and feed whatever is at hand. If all I can get is dirty steel cased I want something that will work like a Glock. So Carbon 15 stays because it is light, but AK & SKS because they will fire a $1.50 or .30 cent round. Different machines, different users and different persons. Great to live in a country where we can actually have conversation about things we can actually have.

  84. I’m a reloader, and am always tinkering with primers, brass, powder and bullets, looking for the optimum load for a given rifle. Friends of mine are competitive shooters with the AR platform, and they are more than willing to try out a new load to see if they can get an edge on the competition.

    One of the things I have noticed in comparing DI vs. OpRod AR-15’s is that the OpRod rifles will reliably function with almost any load. Same goes for the M-1/M1A/M14 rifles. The DI versions of the AR-15 tend to jam if you get too far away from the standard military load parameters. I can’t classify any of the jamming problems as I am not that familiar with the intricacies of the DI function.

    Military shooters tell me that if you change ammunition lots, you have to re-zero your rifle. Is this the case with both DI and OpRod weapons?

    Just my two cents

    1. Germany has replaced the G3 with the G36. HK91s, have issues that keep me from ever buying another one. They are heavy, have increased recoil (which in my youth didn’t bother me), terrible spongy trigger pulls, no bolt hold open device, got quite dirty in the receiver area, and never displayed good accuracy.
      I could never get better than 3.5 inch groups, from a solid rest, with or without a scope. Many ARs will shoot sub-MOA to 1.5 MOA. The only time I saw failures with AR15s was with poorly built reloads. Commercial reloads showed real poor performance. With factory ammo, and I never used steel cased ammo, the ARs always ran. In the Army we obviously used issue ammo (M193 in the mid-80s) and the rifles, H&R built M16A1s, never failed. That was not in combat conditions and only spent 2 weeks per year in the desert. I can own what I want, and settled on ARs with DI for the reason stated in the article. Do you part and they work. I did have AKs that froze-up over night, thanks to rust growing in the gas chamber. It was the residue from steel jacket (copper plated) ammo.

  85. I have several direct impingement AR’s and two Adam Arms piston uppers, including a 10.5″ pistol AR. I use a suppressor on the piston guns and have used it on the DI guns too.

    With the DI guns, a suppressor can cause gas to escape back alongside the charging handle and blast you right in the face. This is due to the pressurized suppressor venting gas out the muzzle more slowly than a non suppressed gun, but also this gas vents back down the barrel – so the volume of gas, even though it may not be carrying as high a level of carbon, soot and fouling as the DI gas and is lower pressure, is still greater in volume than a non suppressed gun. Putting a bead of sealant around the curved mating surface of the charge handle can help, but the piston gun is *much* more comfortable to shoot.

    As to the piston gun “hammering” the bolt carrier, the AA piston uppers have a finger operated valve with several positions – normal, suppressed, and off. In the suppressed position a smaller volume of gas is sent to the piston so the action is not “hammered”.. The off position is useful when you want the minimum sound signature possible, not action cycling at all. The charging handle is used to chamber a new round, much like a bolt action rifle.

    Both DI and piston have their place. I’ve seen no additional wear with the piston ARs.

  86. Piston kits for AR’s are attempting to accomplish something the weapons were not designed to do. The author’s criticisms of the piston driven AR’s are not without merit. However, as the author rightly points out, there are manufacturers who have designed their own piston operated systems that have managed to mitigate (if not eliminate) some of the mechanical challenges presented by trying to fit a round peg into a square hole. And yes, those solutions are pricey.
    To those who sing the praises of the AK, I must agree that in a SHTF scenario where a lone individual or a small band of folks is forced to rely on one system only, this would be the system to go with. NOT because it is more effective, but because it stands a better chance of surviving neglect, hard use and abuse than an AR.
    The AR shines when it is being used by an organization that has the ability and wherewithal to provide the logistical support to ensure functionality and reliability.
    Primitive militias, 3rd world countries and former communist nations went with the AK because they couldn’t or wouldn’t devote the level of support to their troops that most Western nations have or would.
    The AR is by no means the optimal weapon, but with a basic level of support and maintenance it gets the job done most of the time. The phrase “Good enough for government work” certainly applies when it comes to the AR, and for that matter, the AK platform as well. More than anything the two designs serve to emphasize how much socio-political world views impact not just how we live, but how we fight and die.
    AK’s can and do break. I’ve seen it, both stateside and overseas. That being said, if I could only choose one weapon to carry with me in an end of the word scenario and I knew that I would not be hooking up with others of a like-minded nature to form a larger group, the AK would be my choice.
    If I had an inkling that I’d be part of a larger group and that we’d have the long term ability to provide logistical support on a basic level for weapons maintenance and repair, the direct impingement AR would without a doubt be my first choice.

    1. About 30 years ago I had a customer bring in his Chinese AKM. He had shoved his seat back, with a hard motion, and collapsed the receiver. It could have been “hammered out” maybe salvaging it. At the time they were so cheap it was easier to buy a new rifle.
      That came a few years after Nehamia Sirkis told me about he and Galili standing in the Sinai. Galili picked up a Maadi (Egyptian) AKM. He looked it over, dropped it and stepped on the action. It collapsed. He turned to Sirkis and said, “When we build ours it will have a machined receiver”. The did go on to build the Galil rifles. Even those failed after heavy use. They would crack at the rear locking shelf. I had a few of them, and found them to be very solid. I’d take an AR-15.

  87. Since I’m not sure what your talking about it would have been nice to see a few pictures of each system…always like to learn more about each firearm I own …..

    1. If you check Google Images for direct impingement vs piston, you’ll come up with several good explanations accompanied by illustrations or videos.

  88. Reason & purpose exists in all things, to negate one because another is more popular is to do wrong again.
    18 wheels support the total 80K lbs. that the trucks weigh loaded. It was done for volume, weight and somewhat economic purpose, not because it looks or rides cool or reaches a longer distance.
    As for rod vs. gas it’s weather effects on gas vs. rod. Each was built with a purpose in mind.

  89. Rather than try to address the convoluted logic of the “Blogger”, I’ll just stick to some relevant facts.

    The closest design to a DI AR-15 is the MAS-49, but the MAS impingement was indirect, and the gas was not vented into the action. Other than that, every other major battle rifle is piston operated.

    The only DI rifles Gene Stoner ever designed were the AR-10/15. After that, every one of his subsequent designs were piston operated. That speaks volumes.

    Over the years, I’ve heard numerous GI accounts of the AR “jamming”, ie: stop working. Not so the AK’s, they just work. When given a choice between the AK and AR they always choose the AK because of its reliability.

    The AR is VERY high maintenance, especially with full-auto. I wouldn’t want that in a combat rifle because maintenance time is usually not available when you need it most.

    As a hobby shooter, I had heard of so many AR cleaning tasks and problems I opted for a piston on my first AR, and two more since. Absolutely no regrets. I only clean them out of force of habit, never because they actually needed it, and reliability has never been an issue.

    1. @Kent

      I used the M16 platform for many years in the Army, and then for a few more as a security operator in Iraq. I understand what you mean about being a “hobby shooter,” but in my experience the only problem I ever had was with a SBR I was issued during my second contract from 2004 to 2005. It just would not reliably cycle due to the short barrel.

      Other than that, my experience in combat conditions with a good quality M4 is that it works reliably and I staked my life on them more than once, as did the USA and USMC troops we were working with.

      Having said all that, I know there are pros and cons for each system. No question of that, and i will never try to convince anyone to use one or the other unless there is a compelling reason. In this case, there isn’t.

    2. I hope what I write is taken in the same spirit that it is given; objectively.

      Strictly on the technical merits, I think the consensus on what characteristic is the most crucial for any battle rifle is reliability. The rifle simply must go bang each and every time the trigger is pulled, no exceptions. It boils down to a basic life or death thing for you and your fellow soldiers.

      Having said all that, the AK-47 seems to be the reliability standard, not my opinion, but the opinion of many combat veterans I’ve met or read. The AK-47 is their gold standard. The AR, or something like it, should meet or exceed that standard to be our issue battle rifle, with the accuracy of the AR and the reliability of the AK.

      If imitation is the sincerest form of flattery (which it is), then look at the Galil. The Israelis can’t afford to loose a single battle. Everything is on the line all the time whenever they commit to combat, and they have plenty of experience with the AR’s we sent them. So what was their first domestically designed battle rifle without any compromises? An AK clone, following the lead of the Finns who are in a similar geopolitical situation.

    3. The Galil is not in use in any numbers in Israel. The most used rifle/carbine is an AR. Mostly short variants. Israel didn’t design the Galil. They bought 1000 receivers from Finland, used M16 barrel blanks, FN-FAL folding stocks and Stoner 63 magazines. Israel made some cosmetic changes, not drifting far from the Finn RK62. Columbia bought 7.62mm Galils. A failure of the Galil receivers get little attention. They crack at the rear of the locking recesses. The Yugoslavian rifles use the RPK lug system (trunion), as it is designed for more use, and is tougher. The AK has design features that are not the end all in reliability.

    4. Don’t forget the AG42B and its spawn the Egyptian Hakim and Rashad. They are very over complex actions that do not make sense today or in ’42.
      AG42B – 6.5x55mm, the Egyptians in 7.9x57mm and 7.62x39mm. I had the 6.5mm and it never worked reliably. Not due to the DI, but overly complexity.

  90. I carried the most improved version of the M16-A1 in Nam. When I arrived all the bugs had been worked out. The problems encountered were poor maintenance and a lack of spare parts. When I arrived in country the weapon I was issued was one turned in by a soldier on R and R or who had processed out to go home. It was really a piece of junk. The Army tried to issue it to me with out a rebuild after my inspection. The Army stated if the weapon would fire and cycle it would not be rebuilt due to a lack of spare parts. I refused to accept this and refused to go to the field without a rebuilt or new weapon and a kit of spare parts for my platoon. I figured if my issue weapon was that sorry I would need to rebuilt those in the platoon I was to command. After a three week stand off the Army relented and I got a rebuilt weapon and all the requested parts. During my tour are weapons always functioned properly , even with hard combat use and a very dirty environment. They did require constant cleaning after use and frequent inspection for any suspect parts, which we promptly replaced. I did not experience one failure during my infantry tour. Our most frequent problem was a cracked buffer group. If replaced as soon as noticed it did not cause any failures to fire. We checked our weapons daily. I had great faith in my weapon and was confident it would work if religiously inspected, maintained and cleaned. It was definitely not a weapon I would want to carry if a peasant soldier or if spare parts were not available. We were heavily loaded when in the field and I liked being able to carry 50 magazines of 5.56, as we often needed same as resupply was sketchy during contact. Had I been carrying a 7.62 do not think I could have carried such a basic load. On several engagements got down to one mag before issue resolved so light weight of weapon and ammo most appreciated. Direct gas system simple and less parts to maintain and worry about. If you took care of it , it would take care of you.

    1. @Old Soldier

      Thanks for sharing that. People whose entire combat experience consists of great movies, SOF Magazine, and trips to the range just don’t have the credibility someone whose seen the bear has.

      I entered the US Army in the late 70’s and never found a reason to complain about my M16, but I never got into combat until I was a civi security operator in Iraq in 2004. Still, I never found any reason to complain about the M16. Many of the early issues were more due to a poor powered formula than to the weapon design.

      So, while I know the gun gurus say the piston design is better, the military does know what it’s doing when choosing the weapons it sends troops into war with. This has been [proven with the Ma Duce, M4, and many other weapons.

  91. A lot of heavy argumental statements made here. What are the authors credentials to make such charges?
    Why do 3-gun competitors prefer the reliability of the piston systems over direct impingment/ — one word, reliability !
    Aswk the guys who have used the direct impingment weapons in combat on what they trust.
    The M1 and the M14 blow all sorts of holes in the DI concept. Go back and study what the politics were when Stoner invented the AR system!
    This writer is trying to do some pot-stirring for unterior motives, I believe!

    1. Bob M.,

      What high level 3 gun competitors are using piston systems? I hit quite s few matches and a few major matches and piston AR’s are few and far between. The DI system AR is the primary rifle of the sport by a wide margin.

      I’ve used several piston AR’s (5.56 and 308) over the years and owned a few. Overall some are nice but generally speaking they don’t offer anything that you can’t do with a DI gun. Just comes down to preference. However you are not likely to see many in 3 gun as all the ones I have used recoil a lot more than a DI gun and most high level shooters are running custom DI guns with adjustable gas and light carriers anyway.

    2. 3-gun competitors prefer piston guns? Maybe at your range, but the top competitors still use DI. Why? Accuracy. There are several reasons why the DI guns are generally more accurate; absence of piston induced barrel torque and more consistent cyclic rate being the most influential. As far as reliability, DI guns don’t take constant cleaning. I have fired thousands of rounds between cleaning. Simply keep a DI gun oiled and it won’t stop.

    3. “This writer is trying to do some pot-stirring for unterior motives, I believe!”

      I think you nailed it, Bob. The whole article is just a lame attempt to get some interest and page views with a controversial topic, using a title and opening teaser lines with an intentionally bogus premise.

      Everyone who knows anything about rifles in general and especially ARs in particular, knows that piston/op-rod systems are inherently more reliable than DI systems. Not that modern DI systems are UNreliable, just that they are definitely LESS reliable.

      Pathetic article.

    4. Don’t forget that the poor performance of the M14, and the makers inability to fix issues, led Sec. Defense McNamara to cancel production. The AR15 was acquired for the AF. After testing, it was adopted as the M16. It worked well when fired with the correct ammo, but the army decided to switch powders, and ruined the rifles and troop confidence. When re-engineered for the ball powder (it was fixed as well) the M16A1 performed well.

  92. Have you looked at the Syrac piston system? It looks very promising & only 1.4oz heavier than DI setup.

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