The base of the primer is stamped "MOD 908" and has a cap chamber in which the brass cap holder is visible. The brass body is flanged at the base and has a short screwthrea-ded portion for assembly in the cartridge case. The plain portion of the body has two rows of flash holes which are inclined at ten degrees towards the base and are closed by a sealing composition. The cap chamber at the base has an anvil formed in it and two flash channels leading into the magazine. The interior of the body is shaped to form a cylindrical magazine and is screwthreaded at the top to receive the brass closing plug. The plug has a central flash hole which is also closed with a sealing composition.

The magazine contains two pellets of gunpowder in a paper wrapper. The lower pellet has a central perforation, the upper being solid. The powder consists of potassium nitra-te 74.4 per cent, charcoal 16.5 per cent, and sulphur 9.1 per cent.

The copper cap is contained in a brass cap holder pushed into the cap chamber from the base and has a 1.8 grain initiator filling consisting of mercury fulminate 18.6 per cent, potassium chlorate 42.3 per cent and 38.1 per cent of antimony sulphide. The filling is pressed to form a cavity corresponding to the shape of the anvil and is covered by a disc of tinfoil without varnish.