Gas-operation is a system of operation used to provide energy to operate
autoloading firearms. In gas operation, a portion of high-pressure gas from the
cartridge being fired is used to power a mechanism to extract the spent
case and
chamber a new cartridge.
Energy from the gas is harnessed through either a port in the
barrel or trap at the
muzzle. This high-pressure gas impinges on a surface such as a
piston head to provide motion for unlocking of the
action, extraction of the spent case, ejection, cocking of the
hammer or striker, chambering of a fresh cartridge, and locking of the action.