Adcor Defense B.E.A.R GI (Gas Impingement)

Adcor Defense is now manufacturing a version of their Brown Enhanced Automatic Rifle (B.E.A.R) rifle that uses standard AR-15 direct gas impingement instead of a piston. The B.E.A.R GI is available with the same forward ambidextrous non-reciprocating charging handle as the piston model, or without it. The B.E.A.R GI Elite model comes with Magpul MOE furniture and a FN-manufactured barrel with M249 rifling. We do not have pricing information at this time.

Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • Cashel

    Hey, can i ask what the benefits of a gas impingement system are? All i know is that is makes the gun way more dirty.

    • noob

      In addition to what Flounder said, stoner’s genius was the realisation that you could use the rear part of the bolt as the “piston head”, and the bolt carrier group as the “piston cylinder”. Gas goes from the barrel through a thin tube, through a small opening in the upper receiver, down an L shaped metal pipe called the gas key and in between the bolt part of the bolt and the bolt carrier forcing the bolt and the carrier apart.

      when the carrier moves back out of battery, the bolt is rotated by the bolt cam pin and unlocks from the chamber lugs and moves backwards, hopefully extracting the spent cartridge case and cycling the action.

      If you set all the parts to “split” in the diagram on the bushmaster site
      you’ll see the gap where the gas goes.

      You’ll notice that the cycling forces are very centred along the bore axis of the weapon. In a piston gun, the piston and operating rod are parallel to the bore axis and will exert a small pull towards that side (or upwards if the gas piston is above the bore) on all the moving parts.

      Also the recoil forces on direct impingement are much softer than a roller locking design for the same cartridge because the bolt carrier group is moving much more slowly.

      the down side is that once that gas key disengages from the receiver during the action cycling any spare gas spews everywhere, dusting everything down with carbon. On the other hand, a HK roller locking action will start spewing carbon everywhere from the moment the round ignites, since the carbon will come blowing past the brass down the flutes cut into the inside of the HK’s chamber.

      all designs are compromises. Some Sudanese AR10s had little holes drilled in the upper receiver around the gas key area to let the spare gas go out into the atmosphere, but you don’t see that feature much these days.

      • Other Steve

        noob explained it excellently.

        The one thing I would add is that a LOT of carbon/lead/crap comes into the action from the barrel when the chamber opens. Especially when suppressed.

        So the people that go into expensive piston AR kits, then shoot suppressed are almost always surprised by how dirty their guns are still getting.

        The other note about this and suppressors is that most DI systems do not have adjustable gas settings for suppressed, so they run with too much pressure/blowback, making the system dirtier.

        With all things equal, meaning you system is running the correct gass pressure, piston is not truly all that much cleaner than DI. It does some with more parts, weight, and parts touching the barrel. And will keep some heat off the bolt, but it’s the 100,000 rounds without cleaning system that some think it is.

        To that point, almost every AR I see is over-gassed from factory and this is just worse when suppressed.

  • Flounder

    Gas is shot directly into the action to cycle it. The reason stoner made it this way is because it means many fewer parts. Thus making it really sinmple and VERY light. Even a piston conversion kit adds weight but keeps the gas out of the action so it runs cleaner. If you want to know more just go to wikipedia. I think it explains it pretty well.

    • W

      the DI weapon being lighter was true in the 1950’s and 60’s, though isn’t necessarily true now. there has been breakthroughs in newer alloys and polymers that allow gas piston weapons to have equivalent weights to DI guns. While the AR15 was a neat rifle in its day, the AR18 was far superior and it is depressing to know it was essentially dust binned in history.

    • Lance

      The AR-18 was rejected by many many military and never was even adopted as a Police Rifle. Piston guns are nice but not necessary. DI is a bit more accurate than most piston weapon due to the fact fewer moving parts when firing.

      • Chase

        I’ve read that it wasn’t adopted mostly because it came to market at the wrong time. Just about everyone in NATO had already adopted a rifle, and also, it was perceived as being a cheaper version of the AR-15. We tend to perceive a lower price as indicative of lower quality, and sadly this was true of the AR-18. No countries wanted a rifle that “wasn’t good enough” for the United States and allies.

        However, I’m not sure that the source I read this in was entirely reliable, so don’t quote me on it.

      • W

        “The AR-18 was rejected by many many military and never was even adopted as a Police Rifle. Piston guns are nice but not necessary. DI is a bit more accurate than most piston weapon due to the fact fewer moving parts when firing.”

        it was rejected because of politics, plain and simple. the AR18 was superior because of its construction, which is composed primarily of stamped sheet metal, and its more reliable gas piston design. it would have made a outstanding service rifle.

  • Buster Charlie

    Here is the ironic bit: Stoner is, as far as I know, the only direct gas impingement system to actually $#!7 in it’s own mouth.

    The French MAS-49, the Hakim, the Ljungman all of these, and a few others I can’t think of, use direct gas impingement, but do so on the carrier NOT inside the carrier/bolt area.

    So it’s rather odd that other modern guns do not use the original DI method, and instead use the odd stoner method.

    • noob

      does it have something to do with the fact that the original gas impingement systems were all tilting breech block designs, while the stoner system used a short throw rotating bolt to minimise recoil and torque?

      it seems that stoner was completely focused on making the only force on the AR10/15 rifle be “straight back” in line with the bore, almost to the exclusion of everything else.

      by the AR18, the focus was cost.

      • Buster Charlie

        I love how I got marked down, for what reason?

        And yes you are probably right about it being ‘in line’ as in, the gas thrust is inside the bolt in line with the bore.

        I can’t comment on the tilting bolt vs rotary bolt, considering how you can manipulate either by hand without much force I can’t see how it would matter either way.

        I suspect stoner wanted it ‘all in line’ as you can see how he hooked up the stock/buffer in the same manner.

        Having said that, I re-state my original, if unpopular point.

        What is the real world benefit of having DI shoot hot carbon and gas into the bolt carrier/bolt pathway itself?

        Let’s focus on guns that are SEMI-DI, in effect… The HAC-7 and Tavor, and I imagine some other guns, both have short gas pistons BUT also have a extended gas tube running the gas to them in order to keep their gas pistons shorter than the AK while still maintaining gas port position.

        The fact of the matter is, the ar-15 still has a gas piston, it’s just part of the bolt proper and the ‘gas cylinder’ is the bolt carrier, the hakim has a ar-18 style gas spigot, it’s just plumbed with a gas tube like the m-16 (except wider I think).

        So again, why go through the trouble of the complicated stoner ‘gas ring’ setup when you could have the gas directly impinge on a ‘micro’ piston or the carrier directly?

    • W

      “So again, why go through the trouble of the complicated stoner ‘gas ring’ setup when you could have the gas directly impinge on a ‘micro’ piston or the carrier directly?”

      you know, Charlie, i remember mentioning this a while ago (i cant even remember now) and am surprised nobody has implemented it. Perhaps it would be the best of both (DI and GP) worlds.

      • Buster Charlie

        Well, not a great example, but the TAVOR uses a combination system so that one gas block can service multiple barrel lengths. If you look at the AK, the aks-74u, the AKM/AK-74 and the RPK or PSL they have a different piston length, and thus cannot use the same carrier.

        Now i’ve seen AK pistols with their carrier cut down, and just a small stub of the piston attached directly above the bolt on the carrier. In this case it was because the gas block was right near the trunnion, but I don’t see why a DI style gas tube couldn’t feed said gas block on a longer barrel.

        Once I get a lathe set up I’m going to attempt to just that, I have a Romanian AK parts kit, I’ll probably steal an ar-15 gas tube, and rig up a test system as proof of concept.

      • W

        and answering your original point, there is no glaring advantage of DI over gas piston other than market availability. there is still a reluctance by many AR15 shooters to use gas piston rifles, so i can only guess that they are offering DI for those people.

    • not a stoner

      i dont think we need to use anything invented by a stoner. ill get the piston

  • noob

    I read a bit about the BEAR at Gunblast. It seems interesting in that the piston gun shoots like a DI gun because the piston cylinder free floated from the barrel and connected to the gas block by a small gas tube.

    I wonder if other piston systems could be “free floated” in the same way by attaching the cylinder to the a similar rail system.

    it would also be cool if the traditional bolt hold open could be disabled, and the forward charging handle had a “HK slap” notch instead.

    also I worry about the “ringless” piston system. once it wears out, you’ll need new major parts, not just new rings.

    • noob

      whoops. the rifle in this article at Firearm Blog is the Gas impingement rifle. Now I feel like and idiot.

      Still, it does have the forward charging handle, so a “HK slap” notch might be a possibility for those who want one.

  • Cashel: Unless you’re running a sub 14-inch barrel with a suppressor, DI is superior in terms of simplicity and accuracy; the idea that pistons run cleaner isn’t particularly true.

    • Other Steve

      I agree with you, esp when suppressed, but still…. hello box of worms.

      • charles222

        Yeah, well, he asked why you’d want a DI gun.

    • W

      well, the carbon has to go somewhere, its just a matter of deciding where: with a DI, do you want it in the bolt/bolt carrier group? or, in the case of gas piston, in the piston and chamber? The fouling ends up in the chamber with both systems, though that still doesn’t change the fact that cooler running bolt carriers are less prone to fail. Nevertheless, it is a trade-off. strengths and weaknesses for both systems.

    • mosinman

      finally, someone who isnt on the piston AR craze lol

    • Richard C. Johnson

      Grab the bolt carrier on a gas impingement weapon after a mag dump. Then grab one off a piston weapon. The difference becomes evident quickly. While civilians may not care, as a US Marine I can tell you, cheek weld gets to be a bitch when your upper starts getting hot.

      These things also have a SAW barrel built by FN in them.

  • I do like the idea of having the charging handle forward; It seems like it’d be potentially quicker/easier to manipulate for the second part of SPORTS; I figure everybody here knows what that is, and if you don’t you should be ashamed of yourself. :p

  • Lance

    Another AR big deal. I would like there piston version though.

  • Cymond

    The BEAR and BEAR Elite are gas piston models. The GI on some models indicated Gas Impingement.

    Gunbroker shows that most complete rifles are in the $1600 range. Factory direct prices for uppers only start at $1000 with most of the models costing about $1200. The few uppers on Gunbroker seem to be a bit cheaper. Factory upper source:

  • Lance

    Trust me ive seen AR-15 and AR-18s shot side by side. AR-18s are not as accurate and or modular as the AR-15, that’s why it failed.