A locking pin extends between the firing pin and primer element of a projectile to prevent their engagement during transport and while within the barrel of the firing device because of the radial abutment of a safety member that will move axially out of engagement only after the projectile has left the barrel of the firing device so that the locking member may move radially outward to arm the device. The safety member may be the radial abutment of the cartridge case tubular wall before firing and the interior surfaces of the firing device barrel during firing, with the locking member preferably being spring urged outwardly. Also, the safety member may be an axially extending pin prevented from rearward movement out of engagement with the locking member by a spacer disc separable upon exit from the barrel or the cartridge bottom piece.