Operation thumb|SIG Sauer MCX Semi-automatic rifles use gas, blow-forward, blowback or recoil energy to eject the casing after a round has been fired, to chamber a new cartridge from the magazine, and to reset the action. This enables another round to be fired once the trigger is depressed again.
Operation thumb|SIG Sauer MCX Semi-automatic rifles use gas, blow-forward, blowback or recoil energy to eject the casing after a round has been fired, to chamber a new cartridge from the magazine, and to reset the action. This enables another round to be fired once the trigger is depressed again.