Abstract: A pointed cap, which is press fit over the opening in the front end of a hollow, cylindrical primer cartridge, has an integral, tubular socket or detonator holder, which projects coaxially rearwardly from the pointed end of the cap. A cylindrical detonator is disposed to be press fit at one end into a socket so that the opposite end thereof projects coaxially in the cartridge over which the cap is secured, and into contact with the explosive material contained in the cartridge. In one embodiment the forward end of the socket opens on a fuse-protecting slot, which is formed transversely across the pointed end of the cap so that a fuse, which projects from the forward end of the detonator, can pass laterally out of one side of the slot and rearwardly along the outside of the cartridge. In other embodiments the pointed end of the cap is closed, and the fuse is curved rearwardly within the cap and passes rearwardly between the edge of the cap and the cartridge.