The primer is identified by the stamping "930" on the base and is of the type in which the percussion cap is not exposed. The brass body is flanged at the base and is screwthrea-ded over the lower part for insertion in the cartridge case. The interior is shaped to form a cap chamber and magazine and is partly screwthreaded to receive a screwed plug which supports the magazine filling and retains the anvil in position. The cap chamber has a base 0.045 inch thick and has a shoulder near the top to support the anvil.

The copper cap is large in diameter and contains a 1.5 grain initiator filling consisting of mercury fulminate 28.4 per cent, potassium chlorate 34.4 per cent, anti-mony sulphide 35.6 per cent and 1.6 per cent of glass. The filling is covered by a disc of tinfoil without varnish.

The brass anvil is a push fit in the mouth of the cap and has a hole through the centre which tapers towards the base. In addition there are two smaller flash holes which are enlarged at the base. The base of the anvil is of unusual shape.

The screwed plug also has a hole through the centre which tapers towards the base.

The magazine contains a pressed pellet of gunpowder with a tapering hole through the centre and is lightly closed by a brass disc. The top of the body is turned inwards to se-cure the disc and a waterproofing seal of varnish applied to cover the disc and the junc-tion.