Firearms

Which Gas System is Best?

AR-15 AK47 leaning against a barnwood fence

It is an old argument, however, we still field quite a few questions about which gas system is better. If you are new to the sporting rifle world, let me enlighten you on this little pickle that AR-and AK-heads fell into some time ago.

AR-15 and AK47
AK47 and AR15

It started when people began to compare the AK-47 to the AR-15. This is no surprise since both rifles are common on opposite sides of the battlefield throughout the world. Most people know that the AK is famous for its reliability. However, accuracy has never been its strong suit. Still, wide proliferation, sales, and lore followed the AK as it spread across the globe and into the hands of every communist regime, rebel militia and foreign backwoods police force on the planet. In Vietnam, warfighters pitted the AK and M16—the military’s version of the AR—against one another. The M16, being a new design, fell victim to poor planning, incorrect powder and almost no training on the required care and feeding of this new rifle. The AK performed well in jungle conditions and subsequently earned the crown as king of all military carbines.

Eventually, the AK ended up in the hands of American civilians, who then had the opportunity to compare them closely to their AR-15s. In their standard issue configurations, the two famous rifles sported a detachable magazine, iron sights, and a semi-automatic action. However, this is where the similarities end. They represent two distinct approaches to carbine design. Mikhail Kalashnikov designed the Soviet rifle with loose tolerances, wooden stocks and handguards as well as simplified ergonomics. The weapon met the standards soviet leaders were looking for. They required a highly durable, inexpensive, select fire weapon they could put into the hands of a conscript with rudimentary training.

Gas Piston System
Gas Piston System

Unfortunately, the Soviet standard-issue AK was not a precision firearm. This is partially due to the loose tolerances, but the AK-47’s strongest advantage—its reliability—is also its most glaring weakness. The gas piston system (GP) keeps heat and fouling away from the chamber, thereby leaving the action to cycle unhindered by burning discharge from the powder. This gas piston system is what gave the AK-47 its famous rugged reliability. When that conscript soldier loaded a new magazine, he had 30 rounds to influence the battle—every time. However, this type of gas piston system causes more felt recoil, since there is a fair amount of inertia pushing back on the action during the case ejection. More felt recoil equals less accurate follow-up shots, especially when used in full-auto. Further, the barrel is not a free-float design, which also lowers accuracy. These two issues, combined with very rudimentary iron sights, work in concert to give the AK its reputation as a bit of a wild pitcher.

Direct Impingement Gas System
Direct Impingement Gas System

The original AR-15s use a direct gas impingement system (DI). This design moves gas from a fired cartridge directly to the bolt carrier, rather than using a piston above the barrel to push the bolt back. I should note, before anyone starts throwing things, that many ARs today are available with a piston gas system. However, you will pay a premium for these designs, and although they may indeed be extremely great products, it was not the original design for the AR platform.

The original DI design has a number of advantages, starting with accuracy. High-pressure gas acts directly upon the bolt and carrier thereby saving weight, lowering costs and reducing the mass of the operating parts. This reduction in mass increases the accuracy of follow up shots since less material is flying back and forth between shots. However, the main disadvantage of a DI system is that solids from the gas condensing on the bolt face and primary operating mechanism cause the breech of the firearm to foul more quickly. The combustion gases contain vaporized metals, carbon and impurities in a gaseous state until they contact cooler operating parts. The deposits increase friction on the moving parts leading to jams. Thorough and frequent cleaning is required to ensure reliability of this type of firearm.

What many fail to mention is the accuracy differences between the DI gas system of the AR, and the GP system of the AK inside 100 yards are in fact minimal. In G. L. M. Kjellgren’s publication, “The practical Range of Small Arms,” Kjellgren found the two rifles have about a 4-centimeter difference in group size at 100 yards with an average military shooter and iron sights. However, we should note that four centimeters could mean the difference in hitting or missing your target.

So, this still leaves us with the burning question, which gas system is better? For the modern AR-15 shopper, both DI and GP systems are available is a variety of configurations and from several manufacturers, so you’ll have to choose for yourself which one does a better job. To be sure, I wouldn’t want to get shot at by either.

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 (27)

  1. Well one problem I keep seeing is the AK47 rifle used for comparison, Russia hasn’t used the 47 or 7.62X39 since 1974. That being said, several gun experts have written that the AK74 puts more rounds on target than he M4, and of course you can take any gun writer with a grain of salt. My own experience with my AK74 is it is definitely an accurate weapon and this without anything done to accurize it, just a stock factory rifle, I would also point out that the polish Beryl is their rifle that is chambered in 5.56 NATO and can be purchased as a similar-auto called the archer, shoots 1 in groups with good ammo right out of the box.
    Since we Americans now have a lot of range time with AK pattern rifles have found that the inaccuracies are due to 3 things, old worn out rifle parts used for assembly, cheep ammo that wouldn’t shoot well in any rifle,
    And more importantly our guys in the armed forces going against combatants that have very pore riflemanship skills, which I think is the biggest reason for people to say AK’s are not accurate. I know the 4 whitetails would beg to argue that my AK47 is very accurate and the coyotes that have fallen to my AK 74 would say the same.
    This is my experience and opinion.

  2. I have experience using these two type of operating systems and my favorite is the AK-47 operating platform (gas piston) , not to give more credit to the AK but for cleaning and simple function the AK has my vote, don’t miss understand me I prefer the AR-15 or AR-10 for long distance, & accuracy shooting but to compare and decide which one is best in my opinion is an answer that will give unique answers by its user, not to get out of the purpose of this post but I also have and use the HK delayed blowback roller-locked principle and this is also a well designed weapon. In conclusion and in my opinion all these type of operating weapon systems give the end user the ability to choose, and experience which one is preferred, my recommendation is to get out to the range or ask your local gun club or friend to see if you can borrow or rent either the AR or AK and then make your choice, I can assure you that what ever choice you make you will not be disappointed !!
    NOTE : I own and have the opportunity to use and have these rifles and I truly enjoy them whenever I take them hunting or just target and sport shooting, good luck with your choice and your right to choose.

  3. I used corrosive russian 7.62 and had my rifle stop firing in semi automode, after a brisk cleaning with pb blaster it was back to normal, i am sure the bolt assy in an ar would gave acted up after that type of ammo, which is easier to clean and get back to running condition is the pertinent question but cleaning is the solid answer, also type ammo or type primer and powder is a consideration, better to have a single shot then no shot when shf

  4. There is a difference discussing which gas system is best vs which rifle is best. I own three AR 15’s and one AK 47. Cleaning piston rifles vs
    direct impingement systems easily reveals residue accumulates at
    different locations. I clean my guns after every range visit. There is little
    residues on the bolt of the AR with 40 rounds of Wolf steel case. It takes
    Far longer to clean the barrel of each system than the bolt group. I think
    In an ideal world, a piston system has advantages, however, I have never
    Had problems with functioning in either system. I hope and probably will
    never be in a firefight and run hundreds of rounds through my guns.
    I enjoy shooting both systems. One AR has a Wylde chamber and 4 pound match trigger. It drives tacks. The Ak is 100 % on 8 inch metal
    at 100 yards with a red dot. My advice, get both while you can and enjoy !

  5. I bought a bushmaster carbine 15 and it was a jam-o-matic. I seldom had a full clip that i could fire without a jam of some sort Steel or brass. Was that the brand? Model? Or price range? Ammo?. I bought a mak 90 AK and flawless feeding with any ammo. Sights suck but ill fix it. Nothing is perfect. In combat id prefer the AK but to coyote hunt the AR. Fun shooting, either, Im just happy to be here. Thankfully i never had to go to combat.! Thank you Vets.!
    Bill

  6. I have and have built more than a few AR15s I have fired thousands of rounds through them. The only time any of my ARs have ever jammed was with Wolf steel. ( I don’t use steel anymore) The only other malfunction I ever had with an AR was a failure to lock on a gun chambered in 204 Ruger, a bit of brass got caught in the chamber after it blew out a primer. Other than that they have been 100% ARs having a jamming problem is a wife’s tail.

  7. The m1 garand and m14 were both gas piston and will out shoot any plastic pop gun ever made. I have ARs in both 223 and 300 blackout and the 300 Blackout will give you the hitting power of the AK with the accuracy of the AR as long as you want to let the enemy get withing 2-300 yards. I still prefer my 03, Garand and M1A. Rather stop them at 500 then deal with them at 200.

  8. So Darren,
    What you’re really saying is that you are a fanboy of the greatest magnitude and not even open to the idea that the AK is more reliable? Even though in your initial reply you laid out a scenario in which you would have to stop and oil the rifle in battle if it starts to give “gum up”. Sounds to me like you just proved the AK crowds point. For the record I own more AR than AK rifles its a fine weapon as I previously posted and my service record is similar to yours as is my time in the field with the AR. The AK I have flatout NEVER had a failure in thousands of rounds, I certainly can’t say that about my AR rifles even with the super slick nickle boron BCG upgrades and dust grabbing oil to keep it wet.

  9. The perception of the AR gas system being unreliable are way overblown. If you keep it wet, meaning well lubed it will run. Cleaning isn’t as critical as most people think. I’ve carried the M16A2 and civilian AR platform rifles in and out of the Marine Corps for over twenty years and with thousands of rounds fired I’ve only had a problem while shooting blanks in the M16. If it starts to gum up, drop a few drops of CLP in the BCG and it fixes the problem 99% of the time. I don’t dislike the Ak platform but I prefer the AR simply because it is what I’ve used since I was 17 and I use it and know it very well, plus I’ve got I don’t know how many mags for the AR plus all the extras so switching to an AK for a perceived marginal increase in reliability doesn’t make any sense.

  10. The AR/M-16 rifle is a fine weapon but it shites where it eats. The piston operated weapons are cleaner and function for potentially thousands more rounds between cleanings. I have both AK and AR systems the AR’s impress at the range but the AK47 is a true bugout weapon.

  11. “If you can’t find the safety at crunch time then all you have is an expensive stick.” Does anyone actually use the safety on an AK? I know I never have. I’ve yet to shoot an AR, though I just ordered one. But, I’ve shot Saigas, WASRs, and VEPRs (all of which are AK variants) in 7.62×39, 7.62x54r, and 12 gauge, and I have to say that they are awesome weapons. All of the shooters in my family have at least one AK platform weapon. They’re extremely reliable and a ton of fun to shoot. They’re also very inexpensive to shoot, since you can get bulk ammo for around $0.20 per round. The biggest advantage though is that none of us have spent over $400 on our 7.62×39 AKs. Good luck finding an AR for less than twice that. Nothing against the AR (like I said, I just ordered one), but if you’re looking for a first military-style carbine, go with an AK. You can always sell it later for as much as you bought it for (yes, AK values are steadily increasing). That way, if you do later take the $1k+ leap for an AR, you’ll know more about the class of weapons, and probably will be a better shooter. I’m definitely glad I took the time to learn more with my AKs before I decided to pick up an AR.

  12. i am a sportsman and have been all my life. i own both weapon systems and enjoy shooting both. my only complaints of the ar system is more cleaning time and expence of ammo. however it is a matchgrade rifle and unmatched on accuracy. my ak is a cheap option to fun shooting. it has never jammed and i ran 6000 rounds through it in a two day shootathon. the ar had two stovepipe jams in 500 rounds. i hope neither need be fired in self defence however if so the ak is going to be my choice if i need to defend my family in a prolonged time frame. if it comes down to a one clip engagement the ar is the better choice in my opinion. both are very good rifles and very effective in differant climates. in 6000 rounds i never cleaned the ak the ar had to be cleaned 2 times in 1500 rounds. either way i would not want to be on the wrong end of either and both are good choices for self defence. i hope everyone enjoys shooting time and please exersize good judgement and proper safety practices. safety is always the most important responsability of all sportsman.

  13. My question is this: 4cm difference in group size at 100yd or 100m amounts to what? It amounts to about a 2″ group versus a 3-1/2″ group at those distances. Hmmmm. Both are Minute of Bad Guy and capable of stopping him beyond 200yd. Battle effectiveness of both is proven.

    So, what is the argument? Make an informed choice, buy, shoot, enjoy!!

  14. the greatest combat rifle ever made was a gas piston system and so was the follow up that is being used in the wars today. Far more powerful then the plastic pop guns our forces are forced to carry. The M1 Garand and the M14. I’m 63 and can still hit 500 yards accurately unsupported with either one and iron sights. So much for the loss of accuracy with a gas piston design. The lessons I learned at Paris Island and the proper use of a sling may help today’s soldiers learn to shoot a piston rifle with accuracy. The pop gun was nice in very short range jungle brush but we aren’t there now!! Go to any apple seed shoot and learn the proper use of the sling and shooting unsupported.

  15. I own two DI systems, one Colt blue lable and one DMPS M-4 build. I have shot the Colt extensively and have never had it malfunction. I took the time to break in the barrel and it is extremely accurate. I have not fired the DPMS yet. I also own two piston-action rifles, an M+M AK and an IMBEL FAL. To round out the collection of battle rifles, I have an HK 91. It is also very acccurate but has a stouter recoil. I’m not at all bothered by recoil so that’s not an issue. I’ve covered all the bases and realize that maintainance is the key to reliability of all firearms.

  16. During my first experiences cleaning the M16 as a ROTC cadet (and later as a smoke generator platoon leader in the early 80s at Fort Polk, Louisiana (the original “Camp Swampy”, and still later on at the NTC in the Mojave Desert) I was struck by how time-consuming it was to do a good job using the typical grunts’ weapons cleaning tools, and I remember making an observation similar to the following to my CO. His response, since I was a potential officer, was something to the effect of “We have to work with what we are given. Maybe you can change that if you get to be a General at the Pentagon. Personally prefer the M14 which I carried in Viet Nam”.

    In the heat of all-out war, a soldier’s first priority ought to be getting enough rest for the next battle, instead of cleaning his M16 to keep it functioning due to the buildup of gas particulates. The M16s vaunted accuracy superiority over the AK47 and clones won’t do a soldier any good if it jams because he was too tired to clean it.

  17. I have extensive experience with the AR platform and I have decided that I will stick to AK-based rifles if there is going to be a comparison between the two.The Colt MI16A2’s that we used in the Marine Corps were terrible for jamming.I have owned a Bushmaster AR-15. I have a buddy that bought a Smith and Wesson AR-15 and DPMS .308 AR-10. Every one of those rifles have had issues. Now, they are good shooting rifles. I sold my Bushmaster and got me a Saiga .223 (a barebones version of the AK74). I purchased the trigger conversion for it and it is just as accurate as my Bushmaster and way more reliable, not to mention that it was all done for half the price of the Bushmaster.

  18. Neither are worth stink if you don’t take em outa the closet on a regular basis and develop the muscle memory for operating it. If you can’t find the safety at crunch time then all you have is an expensive stick. Just like a Harley, any BEM can buy one but being proficient requires practice on a regular basis.

  19. Bill from Boomhower, I think the M70 is a fine choice, but I would suggest keeping it simple: the more add-ons you stick onto it, the greater your chance will be of undermining the strong point of this gun – its basic reliability. As for the choice of platform, I own a couple AR’s and several AK’s in various calibers, and, over-all, I think the AK makes the best choice for a new gun owner, or for gun owners who are not professional soldiers or police and can’t afford to spend the time and money that a professional might have available for cleaning, assembling, maintaining, and learning to effectively use an AR to its full potential. Of the AKs I’ve owned, the M70 seems like one of the best choices for toughness and reliability in a gun that is already tough and reliable.

    That said, I like the AR as well… it certainly has its strong-points as well, and I like both for their their own unique qualities. I, too, wouldn’t want to be shot with either of them, and I’d be just about equally happy reaching for either in an emergency. If you really want to put fancy accessories like lasers and lights on a rifle, though, I think the AR platform lends itself much better to this than the AK. If the AK is the old, reliable, working farm truck of the gun world, then the AR is a bit more of a hot-rodder’s gun: the AK is quite satisfied with being dragged throught he mud to get a job done, while the AR almost begs to be souped-up, customized, fine-tuned, and turned into a delicate and deeply involved hobby. Which one is better depends a lot on who you are and how you expect to use your rifle in the real world. If you aren’t sure, give them both a try and see which works best for you.

  20. Nice article. I like it when people who know about guns break it down and explain it so well. I’ve not quite understood what people like about AKs so much but I think the GP design is pretty smart to keep out the fouling from the chamber. I’ll probably get an AK and an AR, just for good measure.

  21. The wife and I each have our own AR, mine a S&W M&P and her’s a DPMS, both chambered in 5.56. I’ve fired a friend’s AK 47 (not a 74) and found it lacking in ergonomics and accuracy, but then he hasn’t cleaned it in years. Both of our AR’s are tack drivers at 100 yards and I like the name brand aspect of both. And AR’s being so easily customized/personalized is also a factor.

    As for cleaning, we clean both over a few beers after every range visit. This extends the time we spend together and helps her to learn more about her guns each time. Neither of us object to cleaning either our rifles or sidearms…it’s just part of the sport.

  22. Thanks Rob, now that’s interesting to me, as I just bought an AK-47 a couple of months ago. I haven’t even fired it yet. It’s the new Serbian PAP M70 from Century Arms. I’ve never held or fired either weapon before, or even knwn anyone personaly with one I guess. 30 years of hunting with conventional sporting arms, and a closet full of nice weapons designed for such use does little to prepare you for these type of weapons, but with the ripe climate and mindset of the country, and Obama’s very impressive gun sales record the last year or so, I decided that I might finally have good reason to own a defensive weapons platform, something that really kicks it up a notch from 870s, Sweet Sixteens, model 70s, and model 788s. I’d truly never thought about owning one of these military type weapons before, but now the gun show was only a few days away, so when I told my wife I wanted to buy something, she didn’t really protest, so I set about a crash-course on this smart phone, researching all I could to help me make a decision. I’d heard about the problems our troops had with having to learn on the run about cleaning the Stoner gun early on, and these guns were certainly more expensive than the AKs, which influenced me immediately. I’ve always hated having to clean guns too, and upon more on-line research, I found that you could cram mud into the AK, and still fire it. I understand about tight tollerances = more accuracy, and loose tollerances= more reliability so I went down and bought the Century Arms Zastava PAP M70, and though I haven’t fired it yet, feel confident I made the right choice. Nothing wrong with an AR-15 if that’s what you want, my reasons for purchase are primarily defensive, and like you pointed out, there’s not much difference in accuracy in the first hundred yards, so close quarters reliability and a cheaper weapon influenced my purchase. But then, I’m like you, Rob. I wouldn’t want to be shot by either of these battle weapons myself. I’m stocking up on ammo now, trying to decipher which after-market items out there might actually fit my Zastava. I’d really like the MAKO collapsing stock/fore-arm I think, and one of those single-point sling attachments between reciever/stock, and maybe a laser and EOTECH later, down the road. But even with open sights and wooden furniture this thing is very ergonomic, and capable feeling.
    I also just bought a defensive shotgun to pair with the AK. About a month before the AK purchase, I wanted to buy a Norinco 982, which is a copy of an 870. I’ve always loved 870s, and have an old .410 and a light+weight 20, both Wingmasters w/vent ribs and beautiful wood. But, all the local stores around Boomhower were out, and on back order. Then, at the local Academy store, I found the Savage/Stevens 350(think Ithica mod 37). $197.00, and now I have a good complimentary weapon to the AK. It’s very nicely appointed the way it comes, however there aren’t any available accessories for this gun,as with the popular 870 clones. Therefore, I’m still keeping an eye toward the aquisition of one of these in the not too distant future. Century International Arms actually distributes the 982 Hawk as well as my AK, so I figure I can’t go wrong. Being the first to post here, I can only imagine the path of strong language and strong emotion we’re about to start down with this topic of AR / AK. Guess I’m on point. Lock&load guys, let’s see what everyone else has to say. Thanks Rob.

  23. If the question is GP or DI that really depends on many factors. But the fact that the AK is less accurate has very little to do with the cycling system and more to do with the overall design. DI is fantastic in its simplicity and the FN FAL has a short piston system that is on par(or probably slightly better) with the AR in terms of accuracy but fails when it comes to weight.

  24. I’m just an average citizen who thinks I should have a simple gun with few parts and high reliability. Although well placed bullets are great I think a gun that fires every time has a lot of merit too. If it has too many parts the citizen soldiers could screw up at a critical time.

  25. I think I’ll just stick to my GP. My Stag model 3 has never jammed after 4 days of shooting with no cleaning, and was still on target.

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