Say, in a firearm, after giving off a shot, if the barrel were to be closed off, does there exist a way to store some of it in an external pressure vessel, without requiring a mainly-external source of power and complex machinery?

Forgive the possibly stupid question, I'm a bit of a layman as far as engineering goes.

  • $\begingroup$ Plenty of assault rifles work by diverting barrel pressure, and without external source of power. What are you ultimately trying to achieve? $\endgroup$ Sep 26, 2015 at 22:51
  • $\begingroup$ It's mostly a contemplation, but the idea was to store some pressure to counteract the firearm's motion when squeezing the trigger. $\endgroup$ Sep 26, 2015 at 23:28
  • $\begingroup$ @Llamageddon like a muzzle break does? $\endgroup$ Sep 27, 2015 at 0:10
  • $\begingroup$ @ratchetfreak Yes, but a muzzle break does it during firing, which is simple enough. What I mean is countering the subtle movements when squeezing the trigger, to increase accuracy for, say, a sniper rifle, by using some of the last shot's power. $\endgroup$ Sep 27, 2015 at 12:25

1 Answer 1


Absolutely. There is a device called a bore evacuator which has been in service for a long time on large caliber guns. Its purpose is to draw combustion gas out through the muzzle after the shot cycle is over, so that said gas (which is usually toxic) doesn't flow backwards out the breech and into the crew compartment (assuming the gun is mounted on a vehicle like a tank or self-propelled howitzer). The picture below shows a bore evacuator on on an Abrams tank. It is the bulge in the middle of the main gun barrel with the words "99 Problems" faintly visible on it.

enter image description here

The way it works is simple; after the bullet passes the bore evacuator, the high-pressure combustion gas behind the bullet is allowed to flow into the bore evacuator through small holes. After the bullet exits the gun, the pressure in the tube begins to drop, eventually going below the pressure in the evacuator. The gas then begins to flow out of the evacuator into the tube through holes that are slightly angled towards the muzzle. The resulting discharge induces gas flow towards the muzzle and creates a slight vacuum at the breech. When the breech is opened, hardly any combustion gas escapes into the crew compartment due to this forward flow.

The bore evacuator stores the gas for only a few milliseconds, but it should not be difficult to store it longer (a few seconds or minutes) by using check valves. In fact some bore evacuators in service do use check valves at the inlet to increase their effectiveness. I don't know how much gas you need to store, but you may not need to close off the barrel completely; you may be able to harvest enough gas just during the normal shot cycle, before the bullet exits the gun.

There is also a German recoilless rifle called the "Armbrust":

enter image description here

It uses captive pistons to completely hold the propellant combustion gas inside the weapon after firing. It's a one-use weapon though, which may not work for what you're doing.

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    $\begingroup$ Thank you for the excellent answer. I'll probably accept it, but as a personal rule I always wait a day or two. :) $\endgroup$ Sep 29, 2015 at 19:25
  • $\begingroup$ Found some fascinating info about a handgun that uses cartridge-contained captive pistons, brilliant. What I haven't found a whole lot of resources about are bore evacuators - not a single use case outside cannons and tanks, also no easily accessible efficiency info. Intuition says that they should be able to trap up to half the gasses, probably less, in addition to the function of preventing backwards flow(in case of tanks). Should probably dig a bit deeper, but guess I'll ask anyway - can you imagine using them for recoil control in a handgun? $\endgroup$ Sep 30, 2015 at 23:55
  • $\begingroup$ There's a third type of gun that you may find interesting: the recoilless rifle. It is essentially a gun with an open breech, so that some of the propellant gas discharges rearward during firing and counters the recoil generated by the bullet. This may be tough to implement on a handgun though because the gas would hit the shooter in the face. They're typically shoulder- or vehicle-launched so the exhaust gas can be directed in a safe direction. You could look into muzzle brakes too; they don't store gas, but direct it in some other direction than straight ahead to reduce recoil. $\endgroup$
    – Carlton
    Oct 1, 2015 at 0:58
  • $\begingroup$ Also, there are a few good technical papers on the Defense Technical Information Center website regarding bore evacuators. $\endgroup$
    – Carlton
    Oct 1, 2015 at 0:58
  • $\begingroup$ Yes, I'm aware of muzzle brakes, was primarily wondering if some leftover pressure/gas could be used to compensate for hand tremble when squeezing the trigger(even if it's not really so significant), or whatever else. A bore evacuator could be useful for being able to chamber the next round faster, especially with caseless(and as such, not impossible to ignite with some hot gasses) ammo, or even just "more safely". Most of my thinkings is just theoretical considerations as a hobby :P $\endgroup$ Oct 4, 2015 at 2:14

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