Today, Brownells Gun Techs™ Steve Ostrem and @CalebSavant want to settle a debate. Or maybe just stir the pot. The debate among AR-15 fans is that the AR-15 platform actually DOES NOT have a direct impingement operating system. Steve asks the pertinent question: So where’s the piston then? Caleb gets technical and starts by defining terms.
A traditional GAS PISTON operating system – like on the AK series, FN FAL, HK416, or BRN-4 – sends combustion gas through a gas port in the barrel into a sleeve that applies pressure on a piston that pushes on the carrier to unlock the bolt. In a DIRECT IMPINGEMENT operating system, instead of the gas pushing on a piston, it goes down a gas tube and pushes directly on the carrier to cycle it.
The AR-15 works a little differently. The gas goes THROUGH the carrier and pushes directly on the BOLT to move it. The carrier has two holes that vent the gas out of the carrier and out the ejection port. This helps minimize muzzle rise, which can be quite pronounced on a pure direct impingement system. But the big news is that the bolt acts like a piston and the carrier acts like the sleeve. So the AR-15’s operating system really IS a lot like a traditional piston system!
Pure direct impingement rifles like the old Swedish AG42 or French MAS-49 get a lot of carbon fouling on the carrier because the gas doesn’t get vented out like it does on the AR-15. The AR-15’s bolt and carrier still get dirtier than those of a traditional piston-operated rifle, which keeps all the gas (and all the fouling) up front in the gas block.
So the “myth” is not busted. The AR-15 actually is not a true direct impingement rifle because the bolt itself acts as the piston and the carrier acts as the sleeve.
Note to readers: Please click the share buttons above or below. Forward this article to your email lists. Crosspost on your blog site, social media, internet forums. etc.
Merry Christmas everyone! I gotta give a shoutout to Rad Labs 3d for the sweet custom Brownells AR stand. Oh, and if you haven't yet, go watch Violent Night the movie.
Shout out to Caleb’s barber for keeping that man looking fresh AF
So a M1 carbine is really a gas piston design .
IDI…
Improved Direct Impingement
The gas is still directly impinging (impinging: the act or fact of striking or touching something, or the effect produced by this) upon the bolt carrier group. It is just doing so in a way that much improved over the methods of direct impingement utilized by previous designs.
Hi Love your videos. Would you think about discussing the Noreen gas system they use on their AR style 30-06 and 338 models??
An Indirect impingment or semi di system 😊👍
Mind blown
Been getting like three second audio misalignment from Brownells lately. You guys might wanna check it out
Damn, and I just stopped calling magazines clips.
Being impinged seems terrible. I am going with piston.
I say it's a hybrid system, the gas acting on the gas key on the carrier as a DI to exert force to push the bolt back. and the internal piston system pushes the bolt and carrier apart ro unlock the bolt
Hopes for a Happy and Prosperous New Year to one and all…
my question is about the relief holes on the bolt carrier.
if instead of two holes, a cut was made connecting them and removing that material. how would this affect the action of the rifle?
i'd do it myself, but i only got one rifle and zero skills with anything more technological than a pointy stick.
This argument is why "non gun people" – hate "gun people" technically it's accurate but nobody at the party really cares.
Great video, not knocking the content or the argument, just dont bring this up at the next social gathering.
Another direct gas impingement system you do not mention: The Swedish AG42 Ljungman and derivatives (Egyptian Hakim or Rashid). Take a close look at that quirky action. It is a REAL Direct Impingement action and I think just about the only one that makes no apologies or needs explaining.
It's gas impingement. Even with the closing statement. Refers to the "bolt" is the piston, so it's still the bolt 1st . And I wouldn't call it a piston gun when compared to a piston gun. Nice video though
Spicy
Eugene strikes again.
Perhaps call it a modified piston or modified direct impingement system? Since it is neither a true version of either, perhaps it needs its own name.
Don’t forget to put a drop of oil in your piston’s exhaust port to keep your compression rings lubed. Helpful hint from the Infantry side of the house.
Potato- patato…
Gas tubes are cheeper to manufacture than pistons n stuff…
Nice theory….
But mechanically speaking,
it's just an expansion chamber, instead of a pistons.
Interesting knowledge right here, thank you gentlemen!!
Nomenclature has accepted the terms for simplicity of differentiating the types of piston or "gas guns".
Who knew that Steve is a fan of Pitch Meetings? Super Easy, barely an inconvenience!
The AR is a piston system in the same manner that a tomato is a fruit — technically yes, but for all intents and purposes no
Yep ….
They're not piston. Once the gas is in the bolt and the breach is filthy – It's direct!
Stop aggravating people over the festive season!
I would not argue too much about the fact that there is a piston in direct impingement mechanisms because there is actally always some kind of piston-cylinder couple in any self loading firearm. Even in blowback ones where the cartridge case acts as a piston and the chamber as the cylinder and in recoil operated ones where the locked breech acts as the cylinder and the projectile as the piston). The special thing about direct impingement is that the energy conversion of pressurized gas into a moving mass needed for cycling is happening directly inside the bolt carrier and not inside the gas block or the bore. The right way to separate the direct impingement action of for example a MAS-49 and Stoner's design is to add the words short stroke or long stroke as prefixes. Per definition of ordinary gas operated firearms: A long stroke design let's the piston travel the whole distance of the bolt carrier. This is the case for the MAS-49. The gas tube just acts as a stationary piston and the bolt carrier as a mobile cylinder. The AR-10s and -15s are short stroke direct impingement actions because the piston a.k.a. bolt head moves only the distance needed for unlocking inside its cylinder (the bolt carrier). The Bolt then continues it's travel without separating the piston-cylinder couple any further which is 100 % how a short stroke gas operated action works.
Excellent vid.
I prefer the gas to exit outside of the battery which makes for a much cleaner system. Look at all the indestructible gas piston designs… PWS, SigSauer, AK’ so many in every price range out perform a DI.
That was one that was super informative for me at least I’m in the middle of deciding a piston system to go with like the hk416 but I also love the long stroke piston system that PWS uses does anyone have an opinion on primary weapons systems
Maybe a direct impiston system? I just made that up, lol
Seriously though, you are correct and gave the best explanation to date.
Unless your running a non-transferable FA AR, have Joe’s $1.7T budget for ammo, and shoot everyday, a “direct impingement” system will serve you very well. The piston gun is cool and all, but as we add accessories to the platform, you’re better off loosing weight where you can, and carry more ammo – never run black on ammo! Also, as you age not so well like this ole retired combat gruntpa (ABN), you tend to gravitate to lighter systems, lol.
The irony is that the AK would've been the perfect platform for a direct impingement gas system. The tolerances in a AK receiver are such that you could blast propellant gases into it all day with hardly any issues at all on reliability, at most a slightly tighter cleaning schedule.
Now I'm wondering if I have a homemade icecream churn or a homemade icecream bucket !
I noticed a few SDI grads argue over some of your recent ARIC videos about this. I thought it was pretty amusing watching them both cite the same ArmaLite patents and Eugene Stoner to make their cases, but still totally not understanding the other
Just because it has a tiny little chode cup doesn't mean it's a piston.
Wouldn’t the new sig mcm spear then be direct impingement? It doesn’t have that gas key. It has a small gas tube which hits directly on the bolt carrier which moves and unlocks the bolt.