A bore evacuator.

A bore evacuator is as resevoir that holds the super-heated, high-pressure propellant gases produced by the firing of a shell, then releases them as the shell exits the barrel. When not in use, the atmosphere inside the barrel remains the same as the surrounding environment, thusly it is, or nearly, the same inside the evacuator. As the shell passes through, an opening into the bore takes in the gases, containing them until the shell has exited, then releases them while fresh air inters flow in from the open breech. This reduces the chances of these explosive propellents to flow back into the cabin and cause combustion as they mingle with oxygen, though this can still happen if the evacuator is poorly designed. It is becoming a common feature of most modern tanks. A propellant is a material that is used to move an object by applying a motive force. ... A shell is a projectile, which, as opposed to a bullet, is not solid but contains an explosive or other filling, though modern usage includes large projectiles without a filling which are properly termed shot. ... The barrel of a gun or other firearm is the tube, usually metal, through which a controlled explosion is released in order to propel a projectile out of the end at great speed. ... This article is concerned solely with chemical explosives. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ...