A gas pressure switch is provided for an ignition and safety system for ammunition. The switch includes a housing; a piston actuator within the housing, the piston actuator being displaceable from an idle position to a contacting position by propellant gases of the ammunition during use; at least two contact pins that are attached immovably to the housing; a contacting device operatively associated with the piston actuator and located on a first side of the piston actuator, the first side being opposite a second side on which the propellant gases act during use, the contacting device connecting electrically to the contact pins when the piston actuator is in the contacting position; and a locking pin which holds the piston actuator in the idle position until a predetermined gas pressure is reached and which shears off when the predetermined gas pressure is reached, so that the piston actuator can be displaced into the contacting position.