Compensator

It's made by cutting small holes or notches at the end of the barrel. During the shot, gas will escape through these notches, forcing the barrel down, thus controlling large parts of the recoil movement.

A compensator usually increases the bang and muzzle flash.

Com"pen*sa`tor (?), n.

1.

One who, or that which, compensates; -- a name applied to various mechanical devices.

2. Naut.

An iron plate or magnet placed near the compass on iron vessels to neutralize the effect of the ship's attraction on the needle.

© Webster 1913.