Stoner AR-10/AR-15 Direct Impingement Gas System: The Gory Details 

What this is teaching me is that I can annoy long stroke gas piston guys by calling their AK a direct gas impingement design and be "technically" correct

You are technically correct, THE BEST KIND OF CORRECT!

Comparing scripture reading to patent reading is the best comparison I've ever heard for how some people look at the technical details of patents. 10/10, brilliant work as usual!

This is peak BotR. I always love the videos that you use patents to explain things.

Gun pedantry is my favorite kind of pedantry.

Years before the internet I called it an inline gas piston. Putting all the moving parts inline with the bore still seems the best part.

So. Ian at Forgotten Weapons is popularly known as "Gun Jesus." He also advocates that the AR-15 is not actually DI. Bloke has just used logic to thoroughly demonstrate that the AR-15 is DI. Does that make Bloke "Gun Neitzsche"?

For years, I thought the weakness of AR/Stoner style direct impingement was how it is dirty and also brings a lot of heat into the system--some HK416 propaganda didn't help when in the 2000s, they showed a video where they fire an HK416 at full auto and then strip the gun to show how cold the carrier is--but the weakness of the M16 in Vietnam was not really inherent in the design, especially not the gas system, as I matured and found out. It's still quite a stroke of genius to use the bolt itself as a gas piston and the bolt carrier as the moving cylinder. Of course, it makes those components quite dirty, but it has never failed the rifle (like in Vietnam, most of the severe stoppages are due to casehead separation because of dwell time that can be traced to a vastly different propellant specs; and how the chamber was dirty because they were never issued cleaning kits, which can kill any rifle, not just Stoner's design. Of course, the minor stoppages were due a lot to magazine issues which persisted for a very long time). This was why I wondered how the M16 was and still is beloved in my homeland where the early Colt AR-15 sales happened and the British also tested the weapon system in Borneo, all pre-Vietnam (then bought a bunch of M16A1s in a special procurement in 1976, presumably Colt's post-Vietnam overstocks). I do like the claim about how the metered version of the DI system is more flexible to ammunition type, but of course we can never test that claim since it was probably never built or it worked so badly that whatever prototype was built was immediately scrapped and never mentioned again (though if the latter is true, some documentation may have existed)

I have to admit that you have convinced me that the term direct impingement is in fact a meaningless term probably created more for marketing than engineering.

Some "sharp tongues"/"langue de vipères" were like "this new platform is worth less, they will have all the same point of view", you and Ian and Henry proved you have NOT the same point of view on that, and even better : there isn't drama about it!

One phrase I do take exception to is, 'The AR poops where it eats'. Watch an AR slo-mo and you can clearly see where the gas is vented out of the carrier through the ejection port into the atmosphere. The process of extracting the fired cartridge case from any firearm will suck residual powder gas from the chamber and barrel to deposit crud into the receiver. Even my AK gets fairly dirty there after firing.

I don't disagree with your thesis - I don't think I'm qualified to do so :) However, if what Stoner himself said matters, and looking beyond his "true expanding gas system" comment in the patent, he did also in his interview with Ed Ezell of the Smithsonian (58mins in) say: "...a lot of people have the mistaken idea that this is similar to another system that used a gas tube coming back…escapes me now what was the name of that [Ezell: the Ljungman] yeah Ljungmann type, the Ljungmann type though actually made this gas tube came back and actually blew in a little recess in the bolt carrier and pushed right up here, back on the bolt carrier. This doesn't do that this is just a transfer means of getting the gas down in between the bolt and the bolt carrier and that those two elements then make a piston and cylinder, so in effect the actuating forces are directly concentric with the, er, with the cartridge case and the rest of the mechanism". Thus he does strongly imply the argument that you address herein :) I think it would be best to refer to the "Stoner gas system" or "operating rod" vs "non-operating rod" systems, since Stoner's states purpose per his Ed Ezell interview (58mins in) was to avoid directional forces as far as possible and to help save weight, with the Garand as his what-not-to-do baseline. Either way "direct (gas) impingement" is probably best avoided entirely as it merely causes confusion.

Love these patent and engineering breakdowns

So in effect, every gas operated gun has some sort of piston and cylinder. Even in blowback firearms, which could be considered a subtype of gas operation, the cartridge case acts as a piston while the chamber/barrel acts as a cylinder. This leads to the following questions: -who even coined the term "direct impingement" -is direct impingement defined by the lack of an oprod?

I think people imagined a system where the gas tube effectively just hit/pressed against the flat face of a bolt head, pushing it back and venting the gas, right on then and there. And that people didn't realize that there's always a chamber of some variety, that is similar to a miniature Automotive piston. Without a little cave for the gas to flow into and build up a bit of extra pressure, The gas would escape into atmosphere too quickly. This would not exert enough pressure on the bolt area group.

"Most gas-impingementy" is a true technical term.

THANK YOU!! I am so sick of this “trend” of non mechanically inclined YOUNGSTERS “correcting” me because they heard someone on the RU-vid say so! YES! It absolutely IS direct gas impingement! The “internal piston” works more on unlocking the bolt than it does any bolt carrier action! It may help give it just a slight initial push but that’s all. There is not enough force/pressure/push, whatever you want to call it!

BotR encompasses a wide variety of approaches to videography and a huge array of themes. For me, subjectively, this video is at the absolute peak BotR and informational gun videos in general, alongside some of The Chap's more arcane transitional breech-loader output. If I had an eternal favourites list, this would be on it.

Fantastic video! I hadn’t grasped the idea that either the piston or the cylinder can be the moving part. In the Stoner AR *both* the cylinder (carrier) and the piston (bolt) move. 😎 At about 4:40 he glosses over one of the most interesting parts of Stoner’s design to me. When the gas pressurizes inside that chamber created by the bolt and the carrier, it pushes the bolt *forward* at the same time that it pushes the carrier backwards. The carrier starts moving backward and the gas pressure still holds the bolt forward until the carrier moves back far enough for the vent holes to be exposed and release the gas pressure. Only then does the bolt start to move backward. The genius here is that the gas pressure takes pressure off of the bolt’s locking lugs while the cam pin rotates the bolt to disengage from the lugs in the barrel extension. Sorry - I didn’t mean to write an essay. However, I think it’s important to understand that aspect of the system.

Darn it Bloke! Karl on InRange had me convinced that it was a piston system. Now you have back to thinking of it as a DI system. The only constant is that Eugene Stoner was a genius in putting this all together! PS Watched on Ian's app.

Bloke at it again with the long form nerdtent

Guten morgen in die Schweiz. Much awaited, much appreciated looking forward to excellent insights as always from you.

A salty comment to feed the algorithm. An excellent and cogent description using reason logic (and some excellent cut-in bits). You are to be congratulated Senor Quixote 🙂

Thanks Bloke (and Chap) that was indeed delightfully nerdy. I think there is no substitute for reading the available patents and then using the same language that the inventor used.

Wonderfully nerdy. But the fact is that it's impossible to understand these things by reading a book. I've had a ChiComm M14 for 30, yet I've never looked at the gas piston and understood how it meters the gas. I takes an English engineer in Switzerland to explain it to me.

You linked me this video on Twitter and I think I've figured out what it means. Basically it has a piston and it is direct impingement but not a gas piston operator action. I think lol

Pistons go inside cylinders. The OED defines cylinder as “a piston chamber…” it does not make a reference to what moves. I enjoy the nerdery.

I don't think this mentions the main benefit of the Stoner impingement system - the force applied to mechanical components is in line with the bore. So there's less wear on the receiver, less muzzle climb etc. That's completely lost when you turn it into a short stroke system like they often do now. The second benefit is there's less fouling (like you see on all the non-Stoner parts in the video) because gas escapes the system before cooling down. Third benefit - everything can be super light. When in the army we switched from an AK style system (Galil) to an AR-15 style carabine, and first thing you notice is how little there is to clean. Like - how come you don't ever need to clean inside of that thin aluminum tube? On an AK you have to clean that upper tube every freaking day and oil almost every single part Weather or not it's "true" impingement doesn't matter. I think if you don't drill a hole into the bolt carrier from the carrier key it would still cycle, as "direct impingement". But you'd lose all the benefits of the Stoner system, like, it would blow all the gas into the reciever and the force would be applied off-center. BTW it absolutely doesn't matter if the gas tube was on some other angle with the Stoner action, like from the side as in one of the examples. It's "Stoner impingement".

When the AR15 gas tube is energized with expanding hot gas there must be three things happening. The gas is inside the bolt carrier, it's trying to expand and trying to push the bolt carrier rearward. Newton tells me that it must be pushing forward on the bolt head as well as that's at the other end of the void inside the bolt carrier. At the same time the bolt carrier is trying to unlock the bolt lugs by acting upon the cam stud. This all being driven by a compressible gas there must be a moment of hydro-pneumatic equilibrium where you have the rearward movement of the bolt not just delayed by the unlocking of the bolt but by that brief moment of inertia caused by all the energy being in the gas that is deciding which way to go. I think the AR design acts very much like an air filled shock from a mountain bike. I think changing that to a piston driven design (Hk416) messes with the AR15 and makes it beat it self to death. I could be wrong of course as I'm not an engineer. 14:26 14:26

Thank you. A nice bit of firearms nerdery. It surprises me the obsession with this subject. You can either have (relative to each other) a fixed cylinder and a moving piston, or fixed piston and a moving cylinder. The cylinder/piston assembly can either be located in/on/at the working parts and the gasses ducted to them where the force from them directly impinges on them, or the cylinder/piston assembly is located at the gas port and the force from the gasses is carried from the cylinder/piston assembly via an op-rod. What’s all the fuss about?

Got gas? Shirts would be perfect for your merch shop.

Thanks for a very thoughtful, informative video, though in essence this topic is a case of 'Pot-AY-to' vs 'Po-TAH-to'! 😁 Firearms terminology is incredibly fuzzy, on a par with theology and law. 😎 Even after your very thoughtful argument, I still lean towards 'internal piston' for the AR, though I don't get upset with DI, and I now see how the long-stroke AK-style piston can arguably be called a 'long stroke DI system, since gas directly impinges on the piston head. 😉

Great video, you sent this video to me on twitter and god damn i'm glad you did!

Am I wrong for landing solidly in the "does it shoot" school. I see no positive in getting torqued up in semantics.

Love your vids Thank you 👍 By the way, I completely disagree . It’s an internal bolt carrier piston thus the piston rings on the bolt.

Well explained, thank you!

Thanks for the info, always struck me as odd on what the group think definition was.

Darrrrrapppppmahhhhpoooooockuppppp, excellent job explaining it from an educated person finally. Thank you.

Very informative, concidering how dense and hard to read asxpatent documents can be...

I still like this AR-15 oldies. Because it's charging handle look like FAMAS cocking handle.

Can you do one on the AUG, and it's eccentric interpretation of the AR-18 system. I always wondered what would happen if you get some foilage or a pebble stuck between the gas piston and the op-rod.

What some refer to as a "stationary piston" I like to call a spigot, but that's just me.

Great detail review, even I rather disagree. I thing the Stoner's system is rather short stroke system, as the piston is main mean to generate pulse and its movement is mechanicaly limited. Just smartly the piston instead of pushing a bolt carrier it pushes forward to reciever. As it is acting against force from case, it reduces forces on locking lugs during unlocking - that is absolutely genius.

I'm (just) smart enough to not argue with engineers or their lawyers. The thing I really need to know is - does Verusteleka sell good tinfoil hats and will they fit over my glasses?

Time for some Bloke nerdery. 👍

Nice demonstrations. If a Yank might offer one observations at around the 16:00 mark describing two variations, it is said "this" does one variation while "this" does another. I felt I hoped for more clarity over which "this" was part of which system. Recommend instead of calling both "this", specifying which was from which camp / system/ design group . I hope that translates in a positive light.

I don't see a non-moving "fixed piston" as a piston. It transfers no physical movement to the action. It acts as a brace to push off of and as an end of a concave expansion chamber within a moving cylinder. In the case of the Ljungman, it is additionally a valve or portal to deliver the gas pressure into the expansion chamber, a cylindrical cavity milled into the carrier. A "moving cylinder" is a deeply concave piston in function. The m14 piston you show is a deeply concave moving cylinder, that feeds gas through itself similarly to the Ljungman. As you show, it is more efficient in gas usage than the more typical systems which are naturally over-gassed by design in comparison. The most "direct impingement" is a detonation of explosives in the atmosphere. A brick set atop a block of C-4. A rock perched on an m-80. A daisy cutter knocking down a large area of trees. Only a blowback action is close to true direct impingement from the source gas expanding in the bore which impinges on the bullet and the cartridge case. Though the fired case is what becomes a piston in function transferring the gas pressure to physical movement of the bolt. As for locked breech firearms, the expanding gas is contained in the barrel until the bullet exits. It cannot impinge 'directly' on the bolt carrier from the bore to induce unlocking. In the Stoner design, it has to be redirected into a gas tube to run back to and into the carrier to induce movement. That is an indirect path comparatively. Once inside the chamber formed between the bolt and carrier it impinges directly with enough force to begin the unlocking, extraction and ejection movement. The carrier is a moving cylinder or concave piston as well as a bolt carrier. The Stoner IIICCPBCA Indirect Impingement Internal Concave Cylinder Piston Bolt Carrier Assembly? IIICMCPBCA - Indirect Impingement Internal Concave Moving Cylinder Piston Bolt Carrier Assembly? LOL Acronyms be hard. 😆 Bloke, I think I may have been the one to ignite the online debate which became the "internal piston" term first widely applied by Tim at Military Arms Channel soon after I put forth the idea that the Stoner's "DI system" is a piston system. Much like this reply, it was my middle of the night tirade in the comments on one of his videos a year or two ago. I'd had enough of hearing the "DI versus Piston" debates. There are other often used acronyms that i think are wrong or unnecessary. But that is a whole other argument entirely. I need sleep now.

Seems to me that the Stoner system is really really good. Getting away from it for a "piston" design sure appears to be a step in the wrong direction.

Nice job BOTR, it is a pretty simple issue. But, so many panties in a bunch, it's worse than my local laundrette on pensioners' discount day.

Cheers. Please consider your algorithm to be poked 😊

I have a few questions about carbine length gas system. Ive heard that the 14.5 inch barrel is the ideal pairing with a 6 inch carbine length gas system. The reason being it has roughly the same amount of barrel beyond the gas port as on the rifle length system with a 20" barrel. This is claimed to result in the weapons having a similar dwel time. How can this be possible if the gas only has to traverse half the distance in a carbine system? If the gas is delivered to the bolt in less space therefore faster does it not require less dwell time? Im not sure dwell time is the right term but its what ive heard used on this specific topic. My understanding is that the 14.5 inch length was decided on in the 70s. Does the use of modern, heavier, lower velocity bullets not change this equation again?

I can see why the fixed cylinder over the chamber was not adopted. It would result or contribute to the chamber quickly overheating during rapid fire.

Please comment on the following: A Swiss straight pull (Schmidt-Rubin, M11, K31 et al) is a double action bolt and the Mauser is a triple action bolt?

Coming Next: explaining Quantum Entanglement to the dog

Did you happen to see a certain quarrel on the Forgotten Weapon's site?

happy to give the algorithm a nudge for this sort of content

👍

Sound track to nerdisum Gregorian chant methinks 🤔

The true genius of Eugene Stoner is that we can argue how the AR15 works, and I end up more confused about it than when I started.

It's the stoner system. I've often wondered how it would work if you just blocked the gas key and removed the gas rings from the bolt. would it still cycle just using the gas key as a piston?

For the sake of ease, can we not change the definition of "Direct impingement" to: "the piston and/or cylinder directly attached to the bolt carrier group." ?

NaCl. There you go, a salty comment !😂

My AR-15 identifies as a Thompson 1928 using the Blish locking system......

Why is the mag well shaped that way?

AS long as it goes bang and cycles every time I don't care what system is used.

Wouldn't a metered gas system be better when shooting different bullets, and shooting suppressed and unsupressed? My impression is that the force would always be the same, unlike the continous flow gas systems.

So, what happened to the magwell on that AR-10?!

First I want to say great video, but I almost gave up before giving you a chance to explain your opinion I am so biased on this subject. I think you have a great point and I would like to possibly expand on it a bit. Is it possible that "direct impingement" is simply a misnomer, and if we where to carry the idea to completion we would need to break down what would actually be trying to describe when we say direct or impinging. The only system I could imagine that is both direct and impinging would be roller delayed blowback, that is unless we decide that maybe delayed blowback is "case piston"? Keep up the great content.

Sodium chloride

12:00 Motion and speed are relative through out of the whole universe, not just mechanical point of view.

By plain luck, got a MAS44 & AG42B in the 80s, finding them fine rifles. So, they are direct gas impingment?

1

Now, you and Henry from 9 Hole should do a nice long video discussing this. Having watched both, I'm team Bloke.

What the hell is up with that mag well?

A gas tube system in an AR18 would simplify it by deleting 5 parts and lower the cost, suprised no one has done that.

So, the Z-M LR-300 is a Long Stroke Direct Impingement system.

But it isn't true direct impingement.... Maybe it identifies as one. TransDI. /random argument to poke the algorithms.

Heheh, gas toob

The takeaway here is that AFAIK there is no true gas "impingement" gun in existence. They all have some degree of "piston". The percentage of the force generated by impingement of the gas compared to pressure buildup in the feaux gas tube is anyone's guess and would depend on the design. You would need some complicated transient CFD to really be able to tell. Most conventional piston systems would have almost no impingement force. A weapon like the Ljungman would have a much larger share (but not necessarily most) of the force generated by impingement. The AR is somewhere in the middle.

Interesting juxtaposing Biblical reference to the tiny printed text you are comparing it to. Excellent observation.

Eugene Stoner said that the Armalite AR10 and AR15 do not use a direct gas impingement system. You can watch the video in which he is talking with Mikhail Kalashnikov and Edward Ezell whilst saying exactly that.

The Mini14 is more of a traditional DI than the AR15..The AR does have a charged pressure chamber until the bolt unlocks and the gas is vented out the ejection port holes, the two in front and the one in the firing pin bore..AK's also have metered gas pistons..The AK's piston is vented through the pressed lines of the piston (tube) housing..The holes are not necessary with this type of piston tube..The AG42 uses no expansion system of metered gas, but impinges directly to the carrier.. With the AR15, the extractor lifts completely off the case rim (after) the bolt unlocks relying on the residual pressure to hold the case against the bolt face until the extractor lowers back down into the case rim so extraction can occur..Buffer weight effect on dwell time/bolt unlocking time is insignificant..It does effect carrier velocity and carrier bounce..

Now you've done it. Long stroke pistons aren't real and the AK is direct impingement.

Did you know Stoner and Sullivan first saw constant recoil with the STG44 (MP44)?? Sullivan did not invent it..

I still think that is too complex for a military service rifle, that's probably why the AR-18 and the Stoner 63 were made, but the US stood with the Colt, despite the reasons they had, I could've been done simpler, either like the others DI guns or as a piston driven, it would require way less machining and maintenance.

Internal gas piston is still correct. Direct gas impingement is a Hakim or Ljungman where the gas hits the bolt.

Calling the Stoner system internal piston is not incorrect. We can also say that the FAL or AK utilizes indirect impingement. This is all semantics.

It always rubbed me the wrong way when people say DI is actually an "internal piston." 🙄 Eugene Stoner was a very smart man, and the AR10/15 was his best creation by far. But DI is still DI. Just because the gas takes a slightly downward angled path before actually impinging rearwards on the carrier does not somehow magically manifest an op-rod inside the BCG for a split second.

I don’t give a shite about the story. The odd AR-10 I do give a shite about. Is that an assemblage of parts after production ceased? What is the serial number? You have Sudanese bits with Portuguese bits. What the hell is the bbl? It is not Portuguese or Sudanese. The mag well is non standard semi shaped but there is an auto seat. Welcome to AR-10 collecting. You are about 40-50 years too late.

I still wouldn't classify the AR gas system as a direct impingement system. Are they similar, yes. Are they also different, yes. The best way I found to look at these two and other gas systems is that all systems need gas to impinge on something to make the system work. The differences are what help us separate those systems. Direct impingement, directly hits the carrier and the rearward movement unlocks the bolt and cycles the gun. That is direct impingement as we know it. Simple and straightforward. Every other system is a descendant from the DI system. You can make an AR carrier work like a traditional DI system. Looking at this from that point of shows that the AR gas system isn't the same but definitely related. The extra steps to get the carrier to move back and have the bolt unlock are what make the AR system not a DI system. You loose the direct nature of a DI system for a more efficient descendant system. The AR isn't DI but it also isn't a true piston. Its its own combination of many systems. I think it is more appropriate to call the AR gas system an "Internal Hybrid Gas System". Part DI, Part piston, part extra design steps from Stoner.