AR-15 with Bolt Carrier Counter Weight

Robert B. Davies has applied for a patent (#20110209377) for an interesting AR-15 modification. He proposes inserting a spring loaded counter weight into the back of the bolt carrier. This combined with a complicated hybrid spring/hydraulic bolt buffer should, according to the inventor, reduce muzzle rise.

The improved bolt design with counter weight (85) and counter weight spring (98)
The fluid filled bolt buffer system

The patent is to technical for me to comment if this system would work as described or not. It looks to me like it would be a lot less effective than the balanced recoil system of the AK-107 / AK-108 and the AEK-971. Also, the bolt buffer looks to me, a layman, as far too complex to maintain and too costly to manufacture. Still, it has given me a few ideas … 😉

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.


  • Bandito762

    I tried something like this for a college project, but it seemed to make the muzzle climb and controllability worse. The problem is that you would have to tune be buffer springs and counter weights for each type of ammo (bullet weight, powder charge) that you fire or you risk making the recoil worse, and in some cases a lot worse.

  • JMD

    Oh good. More moving parts. If reducing muzzle rise is all a person is after, there are a number of muzzle accessories that already do that extremely well. The Battlecomp series comes first to mind here.

  • Lance

    Wounder will he work with the Army to improve the M-4 bolt and bolt carrier for the M-4 and M-4A1 upgrade they will be doing?

  • Joseph

    Guy’s like this invent/reinvent the wheel, and then a company will grab a hold of the idea and fund a team of engineers to make it more feasible to machine and better as far as maintenance and reliability. Unless he does the improvements himself he will be lucky to get much money out of it, but it is a cool idea.

  • Burst

    Making the AR-15 even MORE unreliable, one part at a time?
    I like this man’s style!

  • Sounds a bit like a system which used to be advertised for hunting rifles when I was a lad: it consisted of a lead cylinder at the back end of a coil spring, the whole lot fitted into a tube which was installed in the stock. When the gun recoiled the inertia of the weight meant that it tended to stay put, so it compressed the spring, storing some of the energy. When the gun recoil stopped the spring pushed the weight back again.

    The effect of this was to reduce the peak recoil blow by spreading the recoil impulse out over a longer period, so it became more of a long push than a sharp kick. The main problem is that it adds weight, which is not what you want in a military rifle. It might be worth it in one of the larger-calibre AR-15 variants, though.

  • Man

    I agree that an after marked modification to make a M16 function like an AK-107 would be optimal. It is at least in theory, the best solution.

  • charles222

    The M4 has negligible muzzle flip to begin with; don’t really see the point of this.

  • elleerre

    Looks… airsofty

  • W

    I’m curious how reliable the system can be when applied in harsh conditions? I think it is a excellent idea to improve the accuracy and effectiveness of the AR15 platform. Perhaps it can also reduce wear on the buffer spring and what effect will it have on carrier tilt of piston rifles?

  • Derek

    Wow, let’s add some more parts!

  • kvalseth

    Tony, isn’t that principle employed in Sullivan’s Ultimax LMG?

  • Flounder

    Dude burst!
    The diagram looks like it adds a million peices to the internals! But my guess is it would be too finicky for anyone who wants a reliable rifle.

  • Laftrick

    An m4/AR is a .223. It’s got hardly any recoil to begin with. With virtually no kick, why bother?

  • RCG

    The only truly significant word in that whole description is “complicated.” I stopped reading right there.

  • Brando

    This isn’t all that different than the cyclic rate reducer in the Ferfrans SOAR guns.

  • Vitor

    I’ve always wondered that the space occupied by the buffer could house something more useful.

    I mean, why the hell a buffer? Just a lame make up for a design limitation of the AR bolt carrier group.

  • kvalseth, as far as I know the Ultimax just has a very long bolt stroke, which comes to a gradual halt instead of slamming into a buffer. Different principle, same effect.

  • Hrachya Hayrapetyan

    The idea itself is very good but a lot of work must be done to improve and simplify it…I agree with RCG concerning “complicated”.

  • Laftrick
    They do it to have great accuracy in full auto. I heard that AK’s balanced action makes it shoot short bursts (2 to 4 shot) extremely accurate !

  • Sam

    As best I can tell, this system is basically a hydraulic answer to the problems of a high-tension buffer spring, with all the compression resistance of such a spring, but without the added disadvantage of slamming the bolt painfully back into position with more energy than necessary.

    It would definitely help reduce recoil involved with the motion of the bolt, but would only be effective if the buffer spring is not already capable of completely countering the bolt’s rearward force. Is it not?

  • brandon

    It has more parts than the BCG!

  • Mike

    Wait, AR15s have muzzle rise? Since when? Only if you’re not using proper technique…

  • ThomasD

    A 20 pound sack of potatoes slung from the front sight would be equally effective and substantially more reliable.

  • Matt

    Yes, can you imagine keep the sand & dust from jamming all that tiny pieces?

    And stripping for cleaning?

    I personally prefer more recoil but additional reliability.

    I easily speculate it will be so effective to jam-reduce recoil to 0!!

  • Logan

    Why not just get a little heavier buffer, slow the cyclic rate a tad and get a little less kick.

  • tornacı

    Stoner’s “Inline” system is most protected lay out for any military rifle
    produced. Projectile and all reciprocating elements during recoil are all
    in line with bore axis and minimizes and even zeroes the muzzle rise.

    AR 15 rifles do not work on “Direct Gas Impingement” system. The Breecbolt is a stationary piston and Bolt Carrier is a moving cylinder over it. The Gas Key is only a transmitter for metered gas for them. This construction is provided for “Inline” placement for gas Cylinder and piston
    with barrel axis as opposed as other “Piston Striked” gas systems which
    placed over or under the bore which to create an unbalanced additional
    reciprocationel movement during recoil as increasing muzle rise.

    In direct gas impingement rifles, gas pressure taken from gas tube lasts
    its task with impingeing the bolt carrier, but in Stoner’s system, gas
    taken from gas tube begins its task as entering into the gas key. Naming
    AR 15’s as Gas Impingement Firearm is a real mistake.

    All new piston striked AR 15 Clones are prone to muzzle rise for their off
    lined construction with barrel axis and this patent application is not
    exception for this rule.