Aren't all guns 'semi-automatic'? At least, all those that are not machine guns? Pull the trigger, gun fires. Pull the trigger, gun fires. Semi-automatic.
Try that with a single shot, lever or bolt action, or a single action revolver.
Semi-automatic means self-loading and self-cocking after firing a round. -- Buckle Up. It makes it harder for the aliens to suck you out of your car.
