gas-operated

Gas-operated describes a mechanism, typically a firearm, that uses expanding gases from combustion to cycle its action automatically.

In guns, propellant gases are diverted through a port in the barrel to drive a piston or bolt carrier, ejecting the spent cartridge and chambering a new round.

This system allows for semi-automatic or fully automatic fire without manual operation between shots.

The military adopted gas-operated rifles in the early twentieth century.