Gas Delayed Blowback Pistols: A Tour of the System

Today we are taking a look at an assortment of gas-delayed pistols, from South Africa to China to Europe. There is one predominant style of gas-delay execution, but also some variations and some substantially different takes on the concept…


  1. Great video, Ian! A nice primer on the gas delayed blowback concept, plus some fun obscurities. The Alien certainly lives up to its name.

  2. With roughly ten centimeters barrel lenght and approximately 250 grams of slide weight… 8 grams of 9mm Parabellum bullet would create a recoil thrust of… Some four milimeters slide backward movement when its leaving away the bore… Which… Still remaining in the safe usage… But… Slide recoiling speed would be high enough to batter itself against to the receiver and harm both pieces during long usage creating tiny cracks and flatten surfaces… The term “Delaying” should remain in that little initial recoiling distance…

    No gas cushion system can provide such a delay within the time when the bullet to leave the barrel…

    From “Steyr GB” to “P7″… All these systems work as a buffer… To slow down the slide speed and soften its stroke… If noticed… Steyr’s gas vent holes are much and larger in diameter than the single one of others…


    • 4 millimeters (or even more here) of slide movement would rupture case immediately, thats why Hi-Point has almost 2x more then this hypothetical 250 grams slide.

      • Thanks for your interest…

        Believe or not… With standart 9mm Parabellum cartridges in simple blowback handguns… Case rupture will not happen even with 150 grams of slide weight…

        If rupture occurs… This should be by the cause of battery off firing…


        Simple blowback pistol barrels… If made wisely… Takes the cartridge case in the chamber with its case back flush with chamber back surface… By means… With a four milimeters slide free recoil… Only four milimeters of case recoils back without support of chamber walls and in fact this distance of initial slide recoil is more than that value since the receiver also acts forward by opposite force of recoil…

  3. If one would design the P7 the way, that the slide could be kept shut by gas pressure (easily obtainable by enlarging the pistons diameter over the caliber of the bullet) one would encounter the problem that the slide would not move the moment the bullet left the barrel, because as soon as this happened there would be no force left to cycle the slide. Recoil force ends as soon as the bullet leaves and if gas pressure drops ind drops in the barrel and in the cylinder. The initial movement of the slide must be there for such a weapon to cycle.

  4. The system can most easily explained by comparing it to a game of pull robe. A simple blow back would be a strong guy pulling on a robe tied around a rock. The goal is to prevent the strong guy (blow back) to pull this rock (the slide) a certain distance in a given time before he runs out of stamina (gas pressure). To ensure this usually the stone (slide) have to made very heavy. But if you get another guy (pressure acing on the piston) bulling the robe in the opposite direction the strong guy (blow back) has to overcome this resistance to and you cold make the stone (slide) lighter. The gas pressure in the pistol that tries to push the case out again the slide (blow back) has to overcome the slide mass and the counter acting pressure.

    But one thing that is often overlooked is, that the slide must move from the get got if it does not following will happen. Give that our strong guy (blow back) is prevented from doing any movement on his robe, because the other guy is as strong as him. He will get tired (bullet leaves the barrel) before he could affect any movement and then leaves together with the other guy (because if the bullet lefts the barrel and the pressure drops in both systems. The blow back force will end to act and the “delaying” force in the piston will and to act at almost the same time. )

    This can be observed in high speed footage the slide does not gain extra speed as soon as the bullet leaves the barrel, because the “delaying” forces drop as well as the acting forces.

    • The AutoMag II pistol in .22 WMR used a version of gas-delayed blowback similar to the GB;

      There were a number of engineering challenges to overcome in designing an autoloading .22 WMR handgun such as extraction problems. The extraction problems stem from the fact that the slow burning rifle powder of the .22 WMR cartridge develops a late peak pressure. This can cause the case mouth to expand and jam in the chamber when fired from a handgun.

      AMT overcame this issue by drilling 18 holes at 90 degrees to the chamber. A sleeve was then welded over the chamber; providing a tiny amount of clearance for the excess gas to escape from the first set of holes on back to the second set, thereby relieving the pressure enough to prevent the case from sticking.

      While the intent was to reduce gas pressure expansion at the leade’, it also delayed breech opening, therefore it is definable as a “gas-delayed blowback”.

      clear ether


      • Thanks eon…

        .22″ Magnum of course needs some level of delay…

        The approach you mentioned… Seems a friction delay rather than gas… Pressure in the case forces the thin case wall to fill inside the rear holes creating a friction delay first… And… When gas pressure reaches the front holes just at beginning the rifling… Rushes backward through the clearance and flattens the dimples as freeing the empty case to move rear…

        Dirty and rather dubious…

      • Intent in AMT was like flutes in HK roller retarded weapons, its possible they couldnt produce the flutes but went with these funky drilled holes.
        I dont see how it could delay anything,even unintentionally.

  5. The Steyr GB has always reminded me of the Browning Auto-5 action, just with the “piston” wrapped around the barrel rather than the magazine tube…

    That said, the gas-operated pistol has always seemed a bit “much” to me… The energy and recoil forces involved in a handgun do not really justify all the added complexity, unless you’re doing like Desert Eagle/Mars inappropriate calibers.

    There’s a sweet spot for everything. Gas-operated ain’t it for handguns of rational caliber. If you’re stuck needing what amounts to an anti-tank pistol? You’ve got other problems, not the least of which is your grasp on reality. And, physics.

    Ya need that much power? You need a different format. Maybe a Carl Gustav…

  6. Overviews on other odd opperating systems?

    Straight blowback 9×19 (or equivalent/better). If nothing else, as an excuse to have Ian handle a Hi Point.

  7. Missing from the complete set:

    “0.” Walther CCP – As mentioned in the video.

    1. Vector CP1

    2. ZVI Kevin (ZP98) a.k.a. Micro Desert Eagle

    Manufacturer’s website:
    – Antonín Zendl: Breech braking system in self-loading or automatic hand-held firearms by withdrawal of powder gases, CZ8409U1, 4th February, 1999.
    – Antonín Zendl: System for braking breech of self-loading or automatic hand-held firearms by withdrawal of powder gases, CZ286917B6, 4th February, 1999.

    3. Network Custom Guns: “Fixed Gas Operated Barrels for the 1911”
    Company webiste:

    • 2. It has barrel ported upwards shy of chamber, somehow I dont think gases actually do any significant braking on slide as its so wide open space around it.

      Last link is very interesting, even more that its not new (2004.! mentioned) but I never heard about such kits, so far.

  8. can we tempt Ian into some slo mo videos of these pistols?

    I’m very much in agreement with Strongarm on the system being a buffer / gas powered spring

    I’d argue that each of these pistols would work safely without the gas assembly being pressurised

    in the smaller pistols the weight of the piston is likely to be a necessary part of the inertia of the recoiling mass, so that mass would probably still need to be there.

    My best guess is that.with slow motion video, there will be no measurable difference in the slide movement up to when the bullet exits the barrel, with or without the gas.

    if I’m correct
    then these are not delayed, they’re indistinguishable from simple blowback , with gas serving to buffer and decelerate the slide in its later travel

    to allow a lighter recoil spring for easier cycling by hand.

      • Might not be; could be wider, but on the face of it… That slide without the gas, delay… Would perhaps not act as a Vg15, in that; it lacks mass. Unlike the Vg15.

        Or a maybe a Hk p7, Steyr not sure; but different gas system.

        Ian weigh your Laugo slide send it to Strongarm. He he.

      • “They’re indistinguishable from simple blowback , with gas serving to buffer and decelerate the slide in its later travel.” How with the lugo (You go knowhere in a Yugo; bit of cold war propaganda there, where did that come from in Playgrounds Maggie T or what & if so how?.) Laugo? Weight – Slide.

      • Too work… I mean nobody has sellotaped a can of Coke to it, the yugo slide works; Ian shot it, good 7k gun.

        You have lost me, it works with the appropriate slide weight to delay opening.

  9. Is there any prior art on a liquid delayed blowback?? It’s something I’ve thought about but never seen anything resembling the idea.

    The concept being that a non-compressible liquid (water?) is used in the area of the gas delayed system such that it would prevent movement for the fractional seconds until chamber pressure dropped.

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