In a magazine-fed firearm, an interruptor is a device which extends into the cartridge loading path during a loading cycle in order to prevent the rounds in the magazine from pressing on and interfering with the round going into battery, or with the action of the bolt once that round is loaded. They are generally found in weapons with internal magazines; most removable magazines are designed such that the magazine rims serve to retain rounds inside the magazine, and only those slid forward by the bolt can travel up past the rim.