Joost, a reader of TFB, emailed us a sketch of an idea he had. He wrote …

The entire idea is basically deviding the pressure that goes trough a single gas-tube trough a dual-gas tube system, splitting the amount of gas 50/50 in the (low profile) gas block, and into the chamber.

The perk of this system is that the heat of the gas isn’t forced upon a singe gas-tube, and thus allowing for a faster fire rate for longer amounts of time.

Readers, how useful would such a system be? If fired continuously  the gas tube of an M4 will heat up and eventually burst, as seen this torture test …

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.


  • Would this reduce the pressure and cause problems cycling? Would it add weight? Couldn’t you just make the tube bigger or add a radiator?

    • You’re right, adding a radiator seems like a much better solution.

      • That’s my feeling, and I bet the main reason people don’t is weight. If you want a man-portable machinegun, just buy one, and don’t try and use a magazine-fed AR as one.

    • Suburban

      Dual exhaust and now an intercooler? I think I’m on the wrong website.

  • pro.0s

    How often do you shoot fast enough to burn the gas tube out?
    If so, why not finned gas tubes (like finned barrels from the old days) or even a water jacket surrounding the gas tube, though that would increase the weight noticably.

  • Stanislao

    How about a piston?

  • Seems like a piston would solve this problem. Recommended M4 max sustained fire rates are ridiculously low(something like 15 rounds/min).

    • Zapp Brannigan

      That recommended rate of fire is probably more so you don’t burn out the barrel.

    • Nmate

      It’ll make little difference unless you’re going to go to a much heavier barrel profile. The old Colt LMGs were suitable for rather large volumes of sustained fire utilizing the traditional AR gas system. On the other end of the spectrum, the MG36 had a really bad tendency to melt. So much so that even HK and their fantastic engineers gave up on the idea.

  • look like a solution looking for a problem. whats the issue with piston system? from what i heard they reduced the whole bursting into flames thing to almost zero.

  • Nadnerbus

    judging from the drawing, it would require a redesign to the front of the upper receiver, as well as the bolt carrier group (double holes for the two tubes, to gas keys in the receiver), which would also require a widening of the receiver internal dimensions to accommodate a double gas key.

    Or, perhaps the drawing is intended as a drop in replacement, and the two gas tubes join into one before the receiver and continue into the gas key like normal?

    Either way, I think it just doubles the number of tubes that can fail, while probably not really addressing any of the short comings of the AR gas system to any great degree.

    Still, very cool to be thinking outside the box and floating new ideas. Keep up the tinkering!

  • exoskeleton

    Hi Joost, I can make a quick CAD drawing of your design for you if you would like. Send your email address to me;, it’s always nice to see in 3D! Keep comming up with ideas!

  • SvenOrtmann

    His design does two things
    (1) Increase the mass absorbing the thermal energy (two smaller tubes will be heavier than a single one with same inner diameter assuming the same resistance to internal overpressure)
    (2) Increase the are for dissipating thermal energy (by contact and IR radiation), albeit supposedly still hidden under a hand guard (which mostly traps and absorbs the energy)

    A much simpler approach (save for a piston) would be to simply increase the mass a bit (as heat sink) and to include channels for transfer of heat to other metal elements of the rifle.
    A release of much thermal energy in front of the sight line would be troublesome (mirage effect, especially with magnifying optics IIRC).

    Another possibility would be a forced torrent of cooling air (akin to the Lewis machinegun), but such designs rarely proved effective.

  • Joost ‘Juice’ Verschoor

    Hi guys, thanks for all the positive and constructive feedback!

    Obviously a piston would solve this problem, but this idea had been hovering around my mind for quite a while now.

    Once again, thanks for all the kind and mature comments, you don’t see those very often anymore on the internet, good to see them here!

    • Dale

      In a short-barreled AR, this could be a very interesting system to keep the operating pressures slightly lower without having to resort to a heavier buffer (a few guys that I know complain about buffer weight when they change from their 10.5″ uppers to a 16″) and also reduce carrier tilt if you had two tubes feeding into effectively two gas keys on the top of the bolt carrier as it could distribute the gasses more evenly. I’d bet that the recoil impulse would be slightly different and maybe a bit more smooth as well for the shorter barreled uppers. Another thought is using dual gas tubes for suppressed/unsuppressed fire and toggling between a dedicated tube for each/a dedicated gas block for each. I’m just brainstorming.

      I do think that the piston system has already addressed many of the problems that you seek to address with your design, but this could also be a great advantage for a long range shooter being able to keep gas pressures and heat down if done right.

      • Dale

        On my first comment about having to resort to a heavier buffer, I meant for the gun to cycle reliably, not necessary that operating pressures would be lower with a heavier buffer-they arent- the buffer just absorbs the force of the bolt carrier moving backwards faster, better. Perhaps a dual gas tube solution would lower the pressure, therefore lower the amount of force exerted on the bolt carrier, no longer requiring an extremely heavy buffer.

    • Definitely seems like a good idea for SBRs. The high pressures that get pushed through the short-length gas systems on those barrels is pretty insane and definitely not part of the original design of the rifle. The lower pressure could be a big problem in carbine-length or full-length rifles though. The hardest part is going to be building a prototype, as it would require altering the bolt to include a second gas-key. But, if you can do that, and then just split the gas-block, it seems possible. But I think you should be ready to encounter reliability issues after altering the carrier.

  • gunslinger

    interesting idea….but bring out the physics.
    1) i can see the front gas block doing a 1 to 2 tubes. no real problem there.
    2) bringing the 2 tubes into the receiver is a problem. do you connect back to 1 at entry so the upper is unchanged? do you mill an integral 2-1 port in the upper????
    3) what about a voulme/pressure calculation? you have double the volume/area for the gas to go through. but i guess since the cross section area would be double, the pressure in each tube would be halved. and coming back in, it would add back up.

    4) what if 1 tube fails? can yo urun off of 1 tube for a short time?

    i must say, i agree with others that either a piston or a heat sink on the existing tube would be better.

    but i do applaud the though exercise. always need people to ask why and why not?

  • yea


  • Zed

    You could have the added benefit with this system of easily adding variability. On one side, use a PRI Fat Boy gas tube and on the other use a regular one. If you add two switches to the gas block to turn on or off either tube, that gives you 4 possible settings (off, regular tube only, fat boy only, or both tubes). You could do this with two regular gas tubes as well, but would only have 3 usefully different settings. The real question would be tuning this to barrel length/gas port size/gas tube length in order to make each setting useful (ie, one for normal use, one for suppressor use, one for use if the gun is too dirty to cycle normally).

  • Ryan

    If the design intent is intended to dissipate more thermal energy by increasing the surface area of the tube, one could also effectively rib the gas tube in a similar way a barrel is. This could easily be added as a drop in on a standard AR.

  • cliff

    A couple of thoughts. First, by doubling the number of tubes, you are improving your friction loss a lot and dropping the pressure in each, at least for a short duration. This may have the beneficial effect of reducing the chance of a rupture even though you now have twice as many parts to fail. However, when you lower the pressure, you also lower the velocity of the gasses, Will that cause soot and unburnt powder to fall out of the airstream and clog the tubes faster? Will it reduce carbon buildup in the upper? Both?
    My second throught is that if pushed the two tubes far enough away from the top of the barrel and modified the vent holes accordingly, perhaps you could reduce the heat waves that some long range shooters complain of.

  • Nmate

    All you’d need to do is make a gas tube out of Inconel and be done with it. Even a heavier profile gas tube made out of traditional stainless will allow for ridiculous volumes of fire. Look at Colt’s LMG (open bolt M16), the gas tube is substantially beefed when compared to the M16.

  • dan

    I Have to point out that this system will not increase the rate of fire of an AR at all, and it may actually slow it down. the factors that effect all auto loading rifles rate of fire is bolt travel distance, the speed at which it travels that distance and the timing on when the bolt is unlocked. this new item will not affect the two main factors time to unlock and bolt travel distance, and by reducing the total pressure in either tube and spreading out the force you may very well reduce the speed at which the bolt travels.

    Secondly this might acutly not work at all because the AR platform needs a certian amount of inital force to overcome friction and spring tension which the new gas system may not be able to generate consistently with the timing of when the bullet leves the barel and corresponding gas pressure dissipates.

  • Rusko

    because you could totally carry that much ammo on you and fire indiscriminately…

  • Mike

    Overcomplicated? Yes
    Not compatible with current AR uppers and BCGs? Yes
    Solves a non-existent problem? Yes
    Adds Weight? Yes

    I’m sorry, I just don’t see the benefit of the system. Its a solution looking for a problem. Thinking up new ideas is always a good thing, but this just seems pointless and if anything detrimental from my perspective.


  • Hunter57dor

    the solution to a bruised thumb is not another whack with the hammer.

    any major squad support weapon uses a piston. why reinvent the wheel?

    the whole point of an AR is NOT sustained support fire. if you are trying to use it like that, its time to grab a different weapon.

  • Daniel E. Watters

    It looks like an off-shoot of Tim LaFrance’s gas tube modification for his M16K. Really, you can get the same effect by using a pigtail gas tube or a “fat boy” gas tube.

  • -V-

    Why use two tubes? Why not use a larger single tube? It would accomplish 100% of the same effect. Plus, thanks to A=Pi r^2, a tube diameter only marginally larger then an existing gas tube, and have the same end effect of doubling gas flow. I think this is one of those things that worth doing for the cool factor, but from form and function, the same result can be achieved with a significantly simpler setup.