How Does it Work: Stoner’s AR System

Eugene Stoner’s AR-10 and AR-15 use an operating mechanism that is often called “gas impingement,” but which is actually a cleverly structured gas piston located within the bolt carrier. Gas is tapped form the barrel and moved all the way back to just behind the chamber, where it enters the bolt carrier. There the carrier and bolt act as the two parts of a sealed piston, and when the bolt carrier moves rearward the cam pin forces the bolt head to rotate and unlock. The expanding gas is then vented out through holes in the side of the bolt carrier. By locating the piston on the same axis as the barrel, the harmonics are improved and the overall weight of the gun can be reduced by using the gas piston elements as mass in the bolt carrier assembly. Contrary to the old adage “it shits where it eats,” the operating gasses are not vented into the magazine or chamber, and the system has proven to be very reliable.


  1. Very reliable, yes, as long as you’re careful about the propellant used, and clan the system carefully.

    Stoner specifically designed the system for sporting-type powders that produce relatively little fouling. When the M-16 rifle was introduced, the Defense Department OK’d the production of 5.56mm ammunition loaded with IMR powder, the same as used in issue .30-06 and 7.62 NATO ammunition, for reasons of economy.

    Even worse, they failed to issue proper cleaning accoutrements, again on grounds of economy, and told everyone the rifle “cleaned itself”. Exactly which PIO came up with this bit of fantasy has never been determined.

    The jamming problems experienced by troops in the field were largely due to these two historically wrong-headed decisions.

    The Congressional hearings on the “M-16 scandal” revealed that once the IMR powder problem was discovered, instead of ordering a change in propellants across the board, the procurement section offered the manufacturers (notably Lake City) a “deal”; produce ammunition with the correct propellant for QC tests, and then once the lot was OK’d, go ahead and keep making ammunition with the IMR loading. Meaning, no matter what the inspectors passed, the troops continued to get thousands of rounds of ammunition which caused fouling and jamming.

    Meanwhile, they were being shot at by enemy troops with rifles like the SKS and AK, based on systems much more tolerant of inferior ammunition quality and even lack of maintenance.

    The AR system is one of the more sophisticated self-loading gas-operated systems of the mid 20th Century. It is neither the most reliable or the most tolerant of environmental factors. It is a precision machine requiring careful maintenance.

    Whether it should ever have been adopted as a “universal” rifle for issue to combat troops remains an open question.

    See Guns of the Elite by John Walter (w/a “George Markham”), Arms and Armour Press, 1987;



    • That’s just dirty double dealing with regards to ammunition procurement! I have it on good authority that many veterans, if not bound by law, would gladly arrange for Army Ordnance’s cronies to become fertilizer for the shooting ranges.

      • Problem is that such approach, beyond pushing “original” flaw, invited another problems as it prompted manufacturers to use cheapest materials/components – not only controversial powder, but metal for cases and primers.

        • At least a part of the problem was that Stoner designed and tested the AR-10 around commonly available civilian propellants and other materials; same with Sullivan’s re-design into the AR-15. The problem was, nobody really took a long, hard look at the full ramifications of the move to mass production for both the rifles and the ammo. Artellerie-Inrichtingen had issues with the AR-10, when they took it to mass production, which is entirely natural with a new weapon. Unfortunately, the arseholes at Springfield and the Ordnance Department did not want to conduct a full field-testing and actual fielding process including working out all the bugs, and essentially shipped a system out to the troops that wasn’t ready for prime-time, as the expression goes.

          Some of the early teething problems were things they could have fixed before sending it out, but they took the line that it was COTS, interim, and thus, didn’t need that. I think the M16 likely holds the record for the longest service of anything initially adopted as “interim”, anywhere in the world. Which, again, argues for the idea that God looks out for fools, drunks, and the American soldier–Because ain’t nobody else doing that, particularly our Ordnance people.

          • So, for me, it looks that anybody finally responsible from transition shelf -> field, was unable to comprehend rifle and its appurtenances (like ammunition, cleaning kit, grease and so on) as whole (as system).
            There was visible lack of synchronization regarding tweaking of various aspect – like for example fact that it was decided that ball powder will be used in production, yet COLT was allowed to use IMR powder, for acceptance tests of rifles. This result in Rate-of-Fire mismatch, meaning that when used “in field” it was bigger, result in increased wear.

          • Just accept that Ordnance was working to sabotage a weapon “Not Invented Here”, and it all becomes clear. They had the M16 forced on them, and the fielding process was basically them stamping their little feet and going “NO”, like nasty little immature and badly-raised toddlers. Which, I have to conclude from the evidence, they mostly were.

          • “accept that Ordnance was working to sabotage a weapon “Not Invented Here””
            Do as you wish, for now I just conclude that man responsible for weapons adoption active in U.S.A during Cold War-era were less careful than their Soviet counter-parts, with latter always having at least one back-up design.

          • Well, the Soviet system was still running on fear of Stalin, held in institutional memory. Screw something up badly enough, and you’d be lucky to go to Siberia. Really major screw-ups got a quick trip to the execution chamber and a Chekist bullet in the back of the head.

            In the US system, you screw up, you move up. Nobody got demoted or fired because of the M14 fiasco, the M60 fiasco, the M73/M219 fiasco, the M85 fiasco, or the M16. Hell, a lot of people actually got promoted.

            Me? I think there is something to be said for Stalin’s approach to things, at least when it comes to national defense matters. Screw up weapons procurement such that your soldiers die in combat due to ineffective weapons…? Yeah; let’s hold ourselves a little lottery further up the food chain in procurement, and if you get the winning ticket…? You get dumped out in the field where those young men gave their lives because of your inferior crap, and you get issued those exact weapons to try and save your life with.

            Problem we have is this: The careerists have no skin in the game, and suffer no consequences for screwing things up.

          • Also there was a lack of chrome plating that made fouling that much more of a problem. Once the design was upgraded, and this became a standard feature–along with field cleaning kits–the jamming issues dropped in numbers–this during the Vietnam war. Wonder how it performed during the two conflicts in the sand box of the Middle East? Any input/data available? I know the M-16 has mostly been removed from active combat units and the similar M-4 put into the supply chain. But since the weapons still use the basic action, and the same ammunition–how are they faring in the face of gritty sand, instead of mud and muck?

    • If you connect the dots, you can make out an outline of an Ordnance ploy to ensure that the M16 was just good enough to work in Vietnam, yet not so good as to prevent adoption of their wunderkind SPIW.

      Personally, I think it was sabotage, pure and simple: They did not want Stoner’s product to become a standard weapon, and they’d done whatever they could, going back to the AR-10, to prevent that. Look at the whole M14 fiasco–“Oh, yeah, it’ll be cheaper to make on the old M1 machinery…”, and with Garand gone, nobody at the Arsenal could make that happen. Not to mention, that tooling was worn and obsolete.

      Had a young man working for me, who was a bit of a gun nut via his uncle, who’d actually worked at Springfield Arsenal about the time the Ichord hearings were spinning up. He remembered watching truckloads of documentation get hauled off for destruction, and a bunch of nervous-looking higher staffers taking volumes of paper home ahead of the arrival of Congressional investigators. Questions he asked, in all innocence, were answered with “Don’t ask, and we won’t tell you things you’ll have to answer to in court…”.

      The whole cleaning kit/non-IMR powder thing is a bit of a crock, as well–The folks at Springfield Arsenal contended that since the AR-15 was an “off-the-shelf” commercial item, it didn’t need proper fielding, it was ready to go as-is. This was one of those deals where the bureaucracy was forced into something, and then “worked to standard”, and didn’t do the right thing, purely out of pique. Stoner wasn’t consulted on a lot of the stuff they did during early production, and was cut out of things. He told them that chrome-plating the bores and chambers was a necessity; they said “Not in the design…”, and the early guns didn’t get the chrome. Same sort of thing happened with the IMR powder issue, although it was semi-justified in that the rifles had been designed around a non-standard powder that was not available in the quantities it was going to be needed in. Stoner later admitted that they should have designed around the standard military powders, but that the IMR powders comparative cleanliness was too enticing.

      Tons of crap went into the M16 that shouldn’t have happened. Same with the M4. All of these weapons were designed in an absence of mind, and only got fixed once they got them into the field and found problems. It took nearly 15-20 years before the problems with the M4 that they’d first identified in Somalia got addressed. And, to add insult to injury, the M4 was never, ever meant to be the primary infantry individual weapon–It was supposed to be a cute little carbine for the support troops, and nobody paid the least attention to the lethality of it with the M855, until the evidence was overwhelming that there were issues.

      The whole thing is nuts. The idiots got us the M16 because their beautiful baby M14 failed the test of combat in Vietnam, the rest of the Army forced the M16 down Ordnance’s throat, so they essentially sabotaged the fielding through malicious lack of attention, and then the A2 was designed to make the perfect rifle for Camp Perry or a Marine Corps known-distance qual range, followed by the infantry glomming onto the M4 as a better solution to their problems, and…

      It’s a litany of accidental horror. The miracle is that we got anything that worked out of it, let alone as good as the weapon eventually became.

      Personally, I think the A2 should have been something more akin to the M27 IAR, with a mid-length gas system on it. Nobody coming out of Vietnam asked for a longer, heavier M16 with more complex sights, but that’s what the assholes gave us.

      • “(…)AR-10, to prevent that(…)”
        Wait, was AR-10 ever seriously considered for adoption by U.S. forces?
        So far I know competitor of T44 was Rifle, Caliber .30, T48 which was licensed production of FN FAL:
        anyway also in this case, fairness of testing might be questioned, as T44 was meticulously prepared for winter test, while Rifle, Caliber .30, T48 was not.

        • “Seriously considered”, maybe not. It was, however, tested. And, the testing was pretty much sabotaged by the Ordnance folk, blowing up one barrel with proof ammunition. Supposedly.

          It’s on the Wikipedia page for the AR-10, and in the Collector’s Grade book on it.

          My take is that if someone had submitted the ultimate, perfect version of the best possible 7.62X51 NATO rifle ever, one that could hit anything out to 1200m, and perform combat livesaving measures for the wounded soldier lucky enough to carry it… Well, they’d have still found a way to adopt what became the M14. It was that kind of testing regime.

          • Supposedly proof-type ammunition? More like they loaded a cartridge full of HE powder instead of regular propellant powder, filled the barrel with instant cement and SMASHED the barrel further shut with a sledge hammer while nobody was looking, and then had the thing self-destruct to “prove” the AR-10 design was unreliable!

          • I have heard that story through the grapevine, but even Stoner wouldn’t corroborate that–The most he’d claim is the proof cartridge thing, or that they’d deliberately used a lot of ammunition that was out of specification.

            I think this does point to a bit of an issue, in that you need to have a set cartridge design to design the rifle around, right down to case material, ductility, powder type, and the pressure curves it develops. If you don’t have all that nailed down, then you’re basically trying to design by drafting something on the wind.

    • Oh, and a personal opinion?

      I think the M16 is just fine, as a combat weapon, in the configuration that I carried and took to war. It has its foibles, but I’d pick one up over an AK, any day of the week. The key issue is that Stoner, somehow, got all the human engineering and ergonomics right, which I find a little baffling, because he never struck me as the sort of guy who’d have the right mindset for that. The AR-15 series weapons are a near-perfect fighting tool, and superior to about ninety percent of the rest of the weapons out there, so far as layout of controls and everything that goes into making a good tool for combat.

      Operating system? It works, and that’s about as far as I’ll take it. I’d prefer something like the AK or AR-18, but I can live with the Stoner impingement system.

      The only real issue I’d correct is the ambidextrity of it all, and the location for the bolt release; I think Robinson Arms (and, I hate admitting that…) put the release right where it should be, accessible to the trigger finger at the bottom of the trigger guard.

      Other than that, the weapon is superior to just about anything else I’ve handled or shot, to include all the bullpup monstrosities. Especially in body armor and a chest harness…

      • The British found that the L85 was a very bad idea for a modern weapon. It’s a right-handed weapon operated by guys who are trained to perform all the reloading actions with the left hand (which made sense with the SLR version of the FAL) and all the important controls are located on the right-hand side or stuck against your armpit. As it were, the M16 beats the L85 in terms of reloading speed and associated situational awareness during the reloading cycle!

        Oh, and if Denny is correct, the proper right-handed AK reload is actually faster than the popular “Hollywood reload.” The latter involves bashing the empty magazine out, slamming a new magazine into the receiver with the AK pointed at the sky, and then swinging the weapon down for racking the bolt, all non-trigger actions done by the left hand. The proper procedure is faster, keeps the weapon pointed down range, and is therefore a great deal less likely to shoot your friend in the kidneys after racking the bolt. Yes, feel free to view this paragraph as a joke.

        • I can’t really say enough bad things about the L85. I’ve got several hundred rounds through one, courtesy of range session during Trumpet Dance with British Army soldiers who had a ton of extra ammo to burn through. The ergonomics on that thing are atrocious, and the weapon was clearly designed by someone who’d never been in a fight with a rifle.

          You can see the issues, just watching the Brits train for close-quarters combat–The videos are all over the web. In front of trainers, the soldiers going through training are shifting their focus from the scene around them, dropping the weapon from the shoulder to load, reloading (which is awkward as hell in the first place…), and then returning to the fight after having lost track of their situational awareness for quite lengthy periods of time. I can’t think of a better recipe for getting yourself killed, or causing a blue-on-blue unintentional shooting because you lost track of what was going on around you.

          With an M16, or any other member of the AR-15 family, I can run that thing in my sleep without it ever leaving my shoulder, or me having to break awareness of my surroundings. The only time I might need to would be to clear it of a jam, which isn’t that often with a properly maintained rifle and good magazines.

          Frankly, if you’re a combat soldier, and you can’t shuck through every magazine on your web gear without taking your eyes and attention off your surroundings, you’re probably going to be dead in short order, and your leaders never should have taken you to combat. Training standards should mean you can do everything with your weapon without having to break situational awareness of what’s going on around you–Reloads and clearing drills should all be muscle-memory, and done purely on instinct.

          • The Osprey book about the SA80 rifle system describes its faults in detail.


            Quite aside from the purely tactical/handling limitations it shares with every other bullpup combat rifle in existence, the fact is that it’s a terrible design, poorly manufactured, and utterly unsuited to its purpose.

            I’ve long suspected that in adopting it, the British government was less concerned with its actual utility than (a) getting it cheap, and (b) figuring that it was sufficiently menacing-looking to keep the peasants in line when waved at them by a glowering “police” type.

            Whether or not it actually worked correctly in the field seems to have been pretty far down their list of priorities, if it even was on the list at all.

            You know you have a problem when troops in the field prefer the M-16 to the SA80, on grounds of comparative simplicity of operation and maintenance and reliability in use.

            About the best thing that can be said about the SA80 series is that it was sufficiently bad that it dissuaded a lot of armies from signing on to the bullpup rifle fad. Which fortunately seems to be going away, like the bad fever it was about two decades ago.



          • There are a lot of really sad congruencies between the SA80 program, and the one that got us the early M16. It’s like the British authorities observed the M16 debacle, and said “Hold my tea, let us give it a try…”, with “it” being ‘effing up a pretty straightforward and simple basic necessity for an armed force.

            Frankly, I’d round up the lot of them, and have them sterilized for the good of the species, and as an “encourager” example to their successors. Whether it was incompetence or malfeasance, I don’t care: The severity of the negative results is enough to convince me that they need to be dealt with, and dealt with severely.

          • D;

            MAS built about 40,000 FAMAS “tromblons” in five years, and the French Army used them until they were literally worn out, mostly because the various French governments just weren’t interested in buying new rifles, period.

            There was also the “pride” factor. The FAMAS was 100% French. That’s not necessarily a bad thing (I don’t want to get Ian mad at me), but it was an “in-house” design from the start. As far as I know, it’s the only delayed-blowback 5.56 x 45mm rifle every adopted by a major army.

            The 5.56 x 45mm NATO round seems to work best in “traditional” gas-piston type actions- depending on your choice of propellant. As HK found out with the G41, it does not work well in other types of self-loading systems.

            The FAMAS system was and is noted for excessive wear due to the rapidity of its action opening. That’s really not something you want in a weapon firing the high-pressure 5.56mm round.

            The FAMAS stayed in service for so long less because of superiority than just because it was “already there”. And nobody wanted to spend the money to replace it with something better.



          • Kirk:

            I think the SA80 debacle arose because the British Army needed a 5.56mm rifle, but could not use the AR18 then being built by Sterling Armaments, because of the institutional hatred Royal Ordnance had for Sterling.
            The dated back to Sterling successfully suing RO when it produced thousands of Sterling SMGs without paying any royalties.

            RO thought they had the expertise to take an AR18 and turn it into a bullpup. It turned out they did not. At the same time, and to compound the problem, the British government realised that RO Enfield was sitting on a fortune in real estate. They therefore made the genius decision to close down Enfield and build a new RO factory in Nottingham, staffed by people with no prior knowledge of firearms manufacture.

            The combination of a new design, based on a rip off of the AR18, and a new factory with staff without experience, inevitably led to disaster, as would have been obvious to anyone who was not part of RO groupthink.

            On the plus side, one can only hope that the people who live on what was RO Enfield enjoy their new houses.

    • “(…)IMR powder(…)”
      There is interesting pdf relating early 5,56×45 NATO cartridge starting at page 34:
      Interestingly double-base (nitrocellulose-nitroglycerine) propellant commonly called ball power used in 1950s fire-arms ammunition of U.S. forces had only one manufacturer.

      Generally main source of problem seems that they developed rifle and ammunition (method of mass production of thereof) in wrong order – I bet if develop method of mass production of ammunition first and weapon for firing it later, would result in smaller chances of similar failures.

      “(…)Whether it should ever have been adopted as a “universal” rifle for issue to combat troops remains an open question.(…)”
      At similar time to AR-15 Winchester developed its “.224 light rifle”
      it never went past prototype stage, but I am wondering it would possibly be more tolerant for powder used (if I am not mistaken it was developed from M2 Carbine which apparently did not “whine” when ball powder was used)

      • Fundamentally, the Ruger Mini-14 uses the same basic operating system as the Winchester .224 Light Rifle. And yes, both were based on the M1/M2 carbine “short-stroke” gas piston system.

        I understand that at least a couple of Winchester’s designers who worked on the .224 project later worked at Ruger and were part of the Mini-14 design team.



      • “I bet if develop method of mass production of ammunition first and weapon for firing it later, would result in smaller chances of similar failures.”

        Exactly – you are spot on.
        But still, it would likely end up where it is now, with perhaps less of initial pains. It would not create any better weapon than it is.

        • It all needs to be thought of as a system, including the tactical principles and operational doctrine it will be used under. It all has to work together, and if you don’t design that in from the front end, you’re going to spend literal decades trying to figure it out and adjust on the fly.

          The M16 came about through a process that was clearly not such an integrated endeavor, because you also have to go back to the previous utter failure, the M14 and 7.62mm cartridge.

    • “(…)Whether it should ever have been adopted as a “universal” rifle for issue to combat troops remains an open question.(…)”
      I would say that if they decided to do so, special care should be given to provide training including maintenance and publishing of well-though pamphlet for giving system, which seems to be lacking:
      At the present time the two major publications providing training and maintenance instructions on the M-16 rifle are the Army field Manual FM23-9, and a technical manual TM-9-1005-249-14. An examination of the manuals indicate unnecessary duplication on one hand, while providing a lack of information and instructions on another. For in stance,
      the field manual fails to contain adequate instruction on stoppages and actions for correction. Also, certain training publications appear to provide. misleading instructions in that the language tends to oversell the reliability of the rifle.

      from page 47 of

      • There was also the infamous “M-16 comic book” manual;

        Written and drawn by Will Eisner of “The Spirit” fame, it includes most of the vital information that was left out of the FM and TM. Not to mention some factual and practical advice that should have killed the M-16 rifle from the start, like the recommended SOP of putting it in a VCI bag and leaving it there until the shooting starts.



  2. Run the AR10/15 op system using blanks if you want to find out how well it preforms when heavily carbon fouled.

  3. Bloke on the Range had a short tutorial on this, compared the two “gas impingement” systems using diagrams on a chalkboard. Nice to see this explained using actual hardware, thank you. I am told these “harmonics” make for better inherent accuracy (rotating bolt + the actual shove on the bolt in line with the barrel + chamber) so long as you have a good-quality floating barrel.

  4. Having a benefit (in mid 80s) of working on several aspects of this rifle as part of my work duties, I dare to claim I have good knowledge of it. Based on that and years of exposure to other weapon systems I came to conclusion I do not feel any particular liking in it.

    Part of commonly cited shortcomings I also add some (very important) manufacturing aspects. Take for example Key, Bolt carrier. This part is notoriously known for being difficult to make due to plethora of very tight tolerances (or better say combination of them) – it makes lots of rejects, yikes! Next is part it mounts into – Carrier itself. When Ian turns it toward the camera take a look how thin is remaining wall between front .563″ bore and magazine lips relief – no more than .040″ – ridiculous. that is only 2 details there is more. Just name randomly – ejector; it will work reliably only with exact spec.spring plus plastic plug behind it. The concept of forged top and bottom halves of receiver is way over the top and exceedingly complex to make. No, sorry, not a rifle for me.

    In my mind this was a haphazard design stitched together on spur of momentary requirement. Just consider this: if Mr. Stoner was considering it so good, WHY he would almost immediately start to work on a brand new weapon system – Stoner 63?? This is definitely clear departure from it!

    Claiming it is “light” because of use of aluminum and polymer is not true either. It has an average assault rifle weight and on top of it does not even have provision for folding butt. Why U.S. army got stuck with it for so long is beyond me. Elsewhere in middle East you see it only is brand new condition in hands of Kurds, other than that is just AK – all the way.

      • Correct. So much less love had Mr.Stoner to feel for it. It was not ‘his baby’ any more. As a matter of fact it was not ever.

      • If you think about it, the AR15 was a group effort pruned on previous design by E.S. If it was one person’s work as it should have been, it might end up lot better. AR10 is not bad rifle for its size and purpose, I feel lot less reservation for it.

        I think Koreans pulled the best out of AR15 in form of K1/K2.

        • Do bear in mind that the K1 uses the Stoner gas system, while the K2 is a long-stroke gas system somewhat akin to the AK. They’re not at all the same weapon.

    • I’ve never seen a carrier fail in that area you highlight. If anything, it’s indicative of the wisdom of the original designers, in that they got the design just right in terms of being strong enough to last, and be as light as possible.

      Only thing I think I’d want to change about the innards of the AR-15 would be to adjust the bolt cam track to give it a bit more dwell time to allow extraction to take place somewhat more slowly. The extractor works just fine, so long as you’re using the original ammo it was designed for–The necessity for that little neoprene pad only came in with the SS109/M855 loads, which tells me that they got the balance out of whack with it all.

      Truthfully, most of the AR-15 issues come from the round–5.56mm is a notorious cartridge for being hard to design around, and when you consider that the AR-15 is an adaptation of a weapon originally designed around the much different 7.62mm NATO, it’s a damn miracle that it works as well as it does. Caliber conversions are neither as easy or as risk-free as people think, and some mechanisms are only suited for cartridges of specific sizes and pressure curves. Witness the difficulties in adapting the roller-delay StG-45 idea to anything other than 7.92X33.

      What I’d like to have seen would be someone doing a clean-sheet ballistic design around what we theoretically know to be true in terms of ideal characteristics for an assault rifle cartridge, and then apply that to Stoner’s design. I’d be willing to bet that you’d wind up with a very nice, very controllable weapon in about the same size class as an M27, which I think is the sweet spot for someone to carry into battle these days.

      I’ve always felt that the 5.56mm cartridge was a bit too small for an assault rifle, but to be absolutely honest, I could no more quantify that than I could my suspicions that the moon is made of green cheese. The data simply isn’t there, in any real way, to make that determination. It’s entirely possible that the 5.56mm is the ideal assault rifle cartridge, and that I’m just prejudiced due to the indoctrination I got from all the old-timers who thought it was crap.

      Me? I’d like actual numbers to be able to tell you all of this. But, I’ll likely never get them.

      • Ok, good comment. I will focus on first paragraph to give you some insight, how it all happened.

        If you make yourself a layout in a plane square to axis of bore and you choose locking lugs at 22.5deg engaging double stack of cartridge with .38″ base diameter, you will end up exactly with proportions as they exist. Now, consider you have in the following portion of bolt carrier where the pressure is present, lot smaller diameter than in front, thus this frontal weakening does not play much role from stress point of view.

        What would concern me, if I came to this as a fresh problem a bit, is heat treatment. Ideally you should have uniform wall as much as possible to prevent cracking and distortion. As you said, there is no known problem and that is luck gone well.

      • Now something about locking pin cam dwell. Yes it is very short which causes little bit of hassle for reliable extraction. But, we have to keep on mind that it is gas pressure, which is just very shortly lasting puff. If you have instead transfer of momentum thru piston, as is more common, you could afford longer dwell and better reliability to boot.

          • You could do that, but so far the LMT and the Surefire improved bolt carrier designs have changed the cam track, because that is the central point that regulates the action cycle.

      • Regarding cartridge/ casing form I have to agree. Something like Brits had at work right after WWII would be better (meaning more pronounced taper). Even when you take 6.5mm Grendel you are pretty close to ideal shape. In general, better are fatter and shorter casing, at least for automatic small arms (7.92x33mm says it best). If you can handle loading, extraction with them is a breeze. At the end it projects into reliability.

        • “(…)more pronounced taper(…)”
          So do not overlook 5,45×39 – note that while Soviets deemed idea of small-caliber high-velocity cartridge as promising enough to implement it themselves, they ended with cartridge of much different case shape.

          • The 556 cartridge case is nearly cylindrical and the shorties like the M4 extract it too early, when the cartridge is still pressed against the chamber walls. Resulting in too much resistance and torn off case heads. The overall longert taking cycle of the proper M16 rifle does not have this problem, so avoids the issues of the nearly straight 556. The soviets gave their 545 cartridge taper, but nor as extreme as the 7,62*39 has, as that has turned out to be a problem for automatic feeding. As if those soviet engineers knew what they were doing and built a purpose designed cartridge. Whereas the 556 is a lengthened .222 Remington case. So a wildcat if you will. With all the problems that come with that.

      • My limited understanding of enhanced bolt carrier groups by Knights and LMT, and possibly others. centers around the extractor, locking lugs and the cam pin. The extractor, as Denny notes has problems with poor tension on the extractor grooves. Using so called lobster tail extractors with two springs and o-rings seems to be the current thought along this line. Changing the locking lug geometry helps along these lines, although at the cost of interchangability. The webbing around the bolt cam pin is too small and cracks so some manufactures have gone to a smaller cam pin. YMMV as you’ve seen more abused BCGs than I.

        From what I can tell given Stoner’s design is that the carrier pulls on the bolt which is slightly out of contact with locking recesses on the barrel extension. Somewhat like not holding a rifle tightly against your shoulder, something has to give. Dwell time could be the answer, but I’m learning.

      • “(…)ideal characteristics for an assault rifle cartridge(…)”
        Ideal depends on environment in which is supposed to be used. Original requirements regarding effective range for 5,56×45 NATO was 500 yards (around 450 meters) – among others to penetrate (one wall) of steel helmet at that distance. That would be enough for rifle to be used during fighting World War III in Europe – problems arise when you need to fire at greater distance, which occur more often in case of machine guns (SAW) than rifle.
        Contrary 7,62×39 was from very beginning developed to be used both in individual weapons and machine guns, ranges up to 1000 m being expected. As 7,62×39 is slower (less flat trajectory) hitting individual target (using single fire) at greater range is harder, but there is greater chance of crippling wound if it happen.
        Anyway, if you need comprise, between them, take look at 7 x 41 LANTAN
        (DISCLAIMER: exact data are still SECRET, so figures given are just approximation)

        • Funny. The Germans played around with a 7*40 mm intermediate cartridge from GECO in the sixties. It is funny how it always gets back to an intermediate cartridge with a caliber between 6,5 and 7 mm for an individual rifle. And then gets stopped for logistical reasons and inertia of already introduced cartrdiges.

    • “(…)In my mind this was a haphazard design stitched together on spur of momentary requirement.(…)”
      As most military weapons it was crafted to met some requirements. Small mass was one of them, which might explain such decision as putting moving part inside stock and cutting steel parts with thin elements.
      Note that after its debut West European countries were apt to adopt 5,56×45 NATO cartridge, but not weapon itself – they decided to develop own weapons (like for example Beretta AR-70/223) which seems to take little if any inspiration from AR-10 or AR-15 and often being heavier than last.

  5. I’ve gone around a few blocks with several service rifles, including the AR-10 and the AR-15 families.

    Eugene Stoner was an aerospace guy before he got into the gun business. THAT is why he included forged alloys, polymers, etc. into his designs; he knew his materials. The “cheap alloy” used in an M16 receiver is, in fact 7075 alloy, not something you get from the corner hardware shop. It is pretty poor as a casting material but excels when forged and machined. It’s part of the Stoner and Sullivan aerospace heritage. Uppers and lowers start life as forgings which gives them an “improved” crystal structure. Then they are machined to finished dimensions. This is NOT something just anyone can rig in their garden shed; it is a mass-production, industrial process. If you ever get to see M-16 lowers being made, it is very impressive. The “one-pass” broaching of the magazine well especially so. The “tractor-feed’ machinery for making the two halves of the magazine is kinda cute, too.


    Good ergonomics. I once owned and extensively used both early and late production models. Even the early “lightweight” ones were quite manageable on semi-auto. Full auto was “interesting”, but MUCH better than the M-14 and about on par with the heavier FAL.

    The later “Portuguese” pattern ones were a huge step up in features, including handling. They were still lighter than many potential competitors like the G-3.


    I spent some years using and servicing M16 and M16A1 rifles. Many of them looked like something the cat dragged in, but still worked. The BIGGEST killer of these was the neglect and abuse heaped on them by troops who had no “cash” investment in a piece of gear that was supposed to help keep them alive. That, and the arrant nonsense absorbed via the rumour mill and general media seemed to incline them to less than satisfactory handling and maintenance practices.

    Oddly enough, if a particular M-16 (or A1) had a barrel that gauged correctly and good springs and magazines, it would perform as advertised, all day long. Then again, this applies to ALL mechanical devices, from small arms to whatever you have.

    My first “civilian” AR was a late-60’s SP-1. The only thing that would stop it was dubious handloads. GOOD handloads, on the other hand? 60gn Hornady HPs into groups averaging 3/4 inch at 100, iron sights over a rest, NO functional problems. And that is with the original, 1:12″ light barrel. Also pretty good with the Sierra 63gn SP, as used in the early days of the M-16 with the USAMTU and other service teams in the “Match Rifle ” events.

    The early ammo problem (a political decision) was compounded by the inadequate training and technical instruction visited upon the troops at the pointy end.

    As for the “steamy jungles of Viet Nam”; the VC took what they could get and they liked the M-16 having seen what it could do. Some years ago, on a visit to that country, I saw an “experimental” M-16 in a museum. The locals had “re-engineered” the lower receiver to take AK mags. Apparently the bolt had likewise been doctored and I was told that it worked but it was only an engineering exercise as AK variants were more abundant. I suspect they had also fooled with the gas tube because of the wildly different peaks and curves of bore pressure between the two cartridges.

    A good “primer” (so to speak) book is “The Black Rifle” by R. Blake Stevens and Ed Ezell, Collector Grade Publications. My second printing example dates back to 1992, so there has been a lot of spent brass under the Bailey bridge since then.

    • Stoner was Marine Aviation Ordnance in WWII, and I believe he had extensive re-purposing working on infantry small arms, to include the Johnson rifles and LMG–Which is where the multi-lug bolt may have come from.

      My guess is that that experience had more formative effect than the few years he worked in aviation engineering…

      • Melvin Johnson was working for Armalite at the time when Stoner initiated work on AR10 (or what immediately preceded it) as a consultant. Thus the idea of multiple lug rotary locking came most likely directly from Johnson.

      • According to his own record, Mr. Stoner after he left military worked at Armalite first on floor with vision (given to him by Mr. Dorchester?) he would later advance into engineering. Mesrs. Sulivan and Dorchester were big fans of firearms; that’s how whole thing took off.

        • I’ve posted twice, now, with links to the sites where there’s verification of the error you’re making, here… So, without a link included:

          “Enter Eugene Morrison Stoner, a former U.S. Marine Corps armorer from Indiana. With no formal engineering qualifications, Stoner had entered the aircraft engineering industry in the late 1930s before joining the Corps, becoming an ordnance officer. Since leaving the service and moving to California, Stoner had been working on a series of his own designs, and submitted several for U.S. Ordnance Corps testing. It was a chance meeting at a gun range with George Sullivan that led to Stoner joining ArmaLite.”

          Stoner did not work at Fairchild before they hired him, and they hired him specifically because of the prototype for the AR-10 that he was working on…

          • Well, most of it is outlined on the internet, but you need to have the interest and know how to navigate the search parameters–Which ain’t easy for folks whose natal language isn’t American English.

            One wonders what the long-term effects on human civilization are going to be, given that the Internet was primarily conceived of and developed in American English. There have to be unintended side-effects and follow-on things from that which will impact things generations from now, quite like the QWERTY keyboard becoming the installed base standard…

    • You mentioned correctly the aero-space background. I came by sheer coincidence (in old country) from same. Yes, the concept of aluminum forging clearly reflects of ‘culture’ of given industry. It is labour intensive approach but is mechanically sound. I am not aware it would be used on rifles before.

  6. Those interested in the development of the 5.56X45 cartridge should check out the archives at “Loose Rounds” blog.

  7. In the M16 when the gas enters the carrier and starts it to move to unlock there must be a equal and opposite small movement of the bolt head forwards which will result in less friction between the bolt locking lugs and the trunion whilst rotating to unlock Hope this makes sense

    • Theoretically it seems so. You may think of kind of “unloading” pressure from locking surfaces. In reality not as much since brass expanded and took much of the space. For proof you look for highly polished bolt lug surfaces caused by instant friction.

      After all, none of other systems uses this “advantage” and functions just as well if not better.

      • Just checked dimensions of one locking lug. Width is 0.10″ (2.5mm) and height approx. 0.11″. On top of it each lug is on backside chamfered about 0.03″ as a lead-in. This reduces actual bearing area; not worth of talking about need for unloading effect in my mind.

        Steel used on AR15 Bolts is high quality Carpenter 158 (basically tools steel intended for molds), carburized and hardened, upon which is shot peened. It is quite involved process and yes, it tends to produce scrap which adds to overall cost.

        • Speaking of metallurgy and steel grades for guns…. oh man, one of my favored subjects!

          I have seen drawings on AK (yes, Michael’s from Rossia) parts. Most of it was a medium carbon steel hardened to between Rc40-45 and phosphate black. Finished-Done! That gives you idea why AK is so inexpensive to make.

        • The C158 steel is also only a band-aid to fix the problem of otherwise the bolt lugs shearing early in the M16. Which came from changing from .222 to 5,56 with its higher energy and thus more stress on the bolt head. The AR-10 bolt head is much beefier compared to the cartrdige and can get away with a cheaper, easier to work steel. Really the story of the M16 (and tehn M4) is a series of applied band-aids to quickly fix problems arising.

  8. There is one more very important item which knowledge of may be gained only by those who worked with it on engineering/ testing side.

    AR15 magazine feed is inherently unreliable. This is due to the fact that amount of engagement of bolt with cartridge, as nested it magazine is very small. We are talking on average about 0.060″(1.5mm). This is under condition of so called GI magazine which has very thin wall and therefore easy to damage which creates another set of issues.

    At around 1990 CDN ministry of defence was interested with replacement of original GI magazine with one made out of Zytel nylon. I was intimately involved in the process and absorbed problematics involved. This plastic magazine (based on patent by Thermold) was not strong enough and lips often broke upon brisk insertion. If thickened, they practically prevented workable engagement. Best solution is to use steel magazines instead and this was proven over many times.

    Now, you can ask question: how come it works on AUG. The answer is simple: the AUG was designed right form scratch for plastic magazine with all due steps in that direction. Its lips are extremely strong. Other makers, such as Beretta or SIG or FN solved the feed by using simple and beefy 2-lugs bolt. Some used plastic magazines (SIG) some did not. So, it is doable but it requires clear line of thought form start to end.

    So, again another serious strike against AR15/M16/M4 design. People who use them in countless variety mostly in ranges may not be aware of what I wrote about and they find them accurate a nearly functionally flawless and that is good to hear. But as a basic military tool they are, IMHO, grossly inadequate. Usual silly remark if I’d stand in front of it when fired is in light of what was said – meaningless.

    • “So, it is doable but it requires clear line of thought form start to end.”
      Wait, what about AK-103 plastic magazine which so far I know, would also work in AKM which original magazine is metal?

      • AKM magazines are quite thick, so there is enough material to work with. Also the feeding path is different from an M16. The jokes about digging trenches with AK magazines or bashing heads in are not totally wrong. And the soviets have worked on plastic magazines of various makes for AKM and AK-74 since the sixites at least. They did their homework.

    • Main reason (apart from vendor lock-in) for the G36 using its fat polycarboante magazines is reliability. M16 type magazines were found unsatisfactory and even the AUG pattern was found to be not good enough. And from my experience I have never seen G36 magazines fail except when dropped fully loaded on a hard surface, because then often the polycarbonate cracks. Feedlips or body. But then this is easy to spot, whereas a bent metal magazine is not easy to spot. Only real disadvantage of the G36 magazien is its bullk and the very early nineties fashion connecting lugs to clamp magaziens together. Though there are also G36 magaziens in circulation that do not have these nubs. Heck g36 magazines even sometiomes work loaded with 31 or even 32 cartridges. though for 32 you have to force the bolt closed on the first charging.

      Also look at all the engineering r&d that was needed to create the modern Magpul Pmag and Lancer and others to make a reliable M16 magazine. Telling how not so good that design is in the first place.

    • You have to remember that the AR-15 was notionally designed around the idea of pre-loaded, disposable magazines. Their lightness was due to the necessity to provide for the impact on the logistics chain.

      It’s a trade-off, that design. I’m not fond of the ergonomics on a rock-in vs. the slide-in sort of magazine, due to the ease of reload. I’d rather have a mag well and the speed you can achieve with one.

      Although, the rock-in type do allow for drum magazines, lessening the need for mag changes in the first place.

      As with anything, it’s all a trade-off. I do wish they’d have left a bit of room for thicker magazine walls in the AR-15, but we have what we have. If Ordnance had done a bit more work on the fielding process, and validated the design features with an eye towards potential future needs and longevity, well… We might not be here. But, that’d be assuming a competent and conscientious Ordnance mob, which we haven’t had since… Oh, I dunno… Before the Hall carbine idea?

      US small arms procurement has always been politicized, and turned towards meeting other needs, rather than those of the American soldier. They pay a lot of lip service to it all, but the fact is, they’re more concerned with things like developing technologies and paying off political faction members than actually doing their damn jobs.

  9. Finally and for peace of mind 🙂 the last and the best – charging handle.

    I read praises how “ergonomical” AR15 is. Really? What is ergonomical on rifle, which in order to charge it you have to remove it form shoulder? If you attempt to do it otherwise you may end up with your teeth knocked out by your own fist. Are you not finding it funny? I do.

    Sure, over generations (by now about three) you get used to it and find it ‘normal’. A habit is like iron shirt 🙂

    • I think the user would get his face away from the charging handle before reloading. The AR-15’s magazine release is a button as opposed to a lever. The downside is the encouraging of popular “Hollywood reloads,” with a right-handed person’s finger on the trigger during a reload while the left hand does the magazine-swap and bolt-racking stuff. How many times did amateurs shoot their friends in the knees that way?

      • Another non-issue, aside from the fact that you don’t point your rifle at people you don’t mean to shoot. Secondarily, during reloads, the right finger stays the f**k off the trigger and adds support to the grip on the rifle by moving up to the top of the trigger guard/lower receiver. You do that automatically, anyway, because you had to hit the mag release at some point, anyway. Booger-hooks stay the ‘eff off the trigger, unless you are firing.

        I honestly have no idea what you’re terming a “Hollywood reload”, because I can’t think of a single instance where I have seen someone who knew what they were about handling one of these rifles up on a screen.

        • Okay, so we’ll call the improper procedure a “gamers’ reload.” The popular reloading cycle depicted in many video games for any man portable long arm calls for holding the weapon by the grip with the trigger hand while the off-hand loads ammunition. When done with a break-action shotgun, the procedure is “unlock breech with thumb, allow barrel to swivel down by gravity, load shells with off-hand, and then suddenly flick barrel back into battery with trigger hand.” When done with a pump-action shotgun, the process looks something like “hold gun pointed slightly above horizon, trigger hand still at trigger, off-hand shoves shells into magazine tube from below, rack the slide to load chamber.” Video game reload for Thompson M1A1: “release spent magazine, slam new one into well, rotate gun 90 degrees or more counter-clockwise while keeping the gun pointed at your next intended victim, pull bolt handle with off-hand while your finger is still on trigger.” And the most ridiculous reloading procedure some idiot proposed to me about avoiding the M1-thumb involves using your left hand to karate-chop a clip into the magazine. I laughed in his face. Yes I’m just kidding…

          • It sounds like everyone is buggering up the 1970s era police-style “SWAT tactical” reload.

            As someone who taught small arms to police (sheriff’s and etc.) in the late 70s and early 80s, I strongly discouraged that reload technique, because without absolute, 100% trigger discipline (which cops are, frankly, lousy at) it’s almost a guarantee of ADs.

            Also, most right-handed people are terrible at using their left hands for anything as involved as ejecting a magazine, inserting a loaded one, and releasing a bolt.

            As for Garand reloads, the safest method (to avoid M1 thumb) is right in the manual; use your left hand to hold the rifle at the balance point, while your right hand is pushing the clip in with the thumb until it latches, and the right side of the heel of your right hand is pushing firmly back on the operating rod charging handle to prevent the bolt from closing.

            People who try to hold the Garand by the stock wrist with the right hand while shoving the clip in with the left tend to find out very quickly why the manual says to do it right-handed.



    • Non-issue. In the first place, you don’t operate the charging handle for most routine reload drills; that’s why you have the bolt hold-open, or you change out a near empty magazine for a full one, leaving a cartridge in the chamber. Even if you do have to cycle the operating handle, you just break your cheek weld enough to clear it, and your left hand sweeps it back.

      You may have worked on these rifles a lot, but I don’t think you got much “stick time” in on them, or received any tutilege from someone who knew how to run them under fire.

      • Ok, you may have point here. I like lively discussion – and do not mind to get stirred up – or even better, stir up someone else 🙂

  10. I think I understand why Ian does not consider the AR type of rifle to be direct gas impingement, but I am not sure I agree with him.

    To my mind, a rifle with a piston has that piston running along the barrel. It is this piston which then operates the bolt or bolt carrier. If the rifle has a gas tube running the length of the barrel, which then feeds gas into the bolt and bolt carrier assembly, then even if this assembly is engineered to act as a quasi-piston, I still cannot call it a piston, or say that the rifle is not operated by direct gas impingement.

    Obviously, this is a question of semantics. I feel that the AR rifle is a direct gas impingement rifle of a different design to a classic such as the MAS49, but still a variation on the same theme.

    There are no absolutes however, it is a matter of opinion.

    • Sounds like kind of ‘deferred’ judgement and I have no problem with that. Playing with words, as you say.

      The key issue is, at least from heat dynamics point of view, that the rifle’s mechanism is burdened with extra heat input in addition to what is already there. Not entirely sensible approach. As a testimony to this conundrum you can observe that no one else repeated that and if they did, it was within licence duration span and shortly after was corrected.

    • I think the AR-10/AR-15 system is best described as an in-line internal piston. Actual direct impingement is the MAS-49 that just blows its tapped gas into a cup in the bolt carrier. the Stoner system has a piston operating inside the bolt carrier.

      And this system cannot be too bad, because the chinese decided to use a similar arrangement in their wz-85 heavy machine gun. In 12,7*106 mm. really, it cannot be too bad if it stand up to that. 😉

  11. AR10 rifle concept should not be based upon the “Best military rifle” approach. lt’s main lay out shoud be creating an autoloading shoulder gun at instant of automatic firing, containing all recoiling and expelling masses joined at along with the barrel axis, therefore minimizing the bore deviations from the aimed point which, realized soon after that, same could be obtained through simple muzzle attachments. Recoil spring in the unfoldable shoulder stock, cocking handle effective only backwards and bolt carrier forcing the mass ratio between the bolt and its nestler should all be constructed and located with this philosophy in mind and changing one of those would spoil the nature of gun as being made in newly rising off center piston samples. The rifle was not truly suitable for military purposes even the time when introduced… Even Mr. Stoner should had clearly seen the fact and designed another better gun suitable for military purposes ascoded AR 18 afterwards.

    • For a weapon “not suitable for military purposes”, it sure has remained in service for a long time.

      My take? It’s more than suitable. Not ideal, certainly, but the damn thing does work, once you understand how to keep it running, which isn’t some esoteric science only conductable by secretive orders of Asian monks. I’ve trained people on it, used it, carried one for 25 years, and it did just fine. I’d still pick one up out of a pile of other options, over just about anything else out there. Valmet M76 in that pile…? Weeeellll… Maybe. I still remember mine with fondness, despite the sh*tty ergos.

      • A rifle with unfoldable stock suitable for fully military purpose…And please do not use words like “monk” for humans…

        • English isn’t your primary language, is it? Rather than take offense, I’m going to point out that “monk” is not short for “monkey”, but rather refers to a religious monastic order like the Buddhist and/or Shaolin monastic orders across Asia, who are noted for their predilection for the martial arts in China and Japan.

          Before taking offense at something said in a foreign tongue, one might want to ensure that one actually understood what was said.

          • Thanks lesson for English language… l am educated and old enough what you mean…

            Offensive… Others may be different, experienced, cleverer and bigger than one’s mind…

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