US Primer, Percussion, No. 12 Mk 2 /L/




This primer may be found in some old rounds of British design. It is screwed and staked into the head of the old M22 or Mk 1 /L/ Cartridge Case. The “L” in British nomenclature stands for land use. The Mk 2 Primer consists of two parts, the head and the body.

The brass body contains the primer charge of 64 grains of black powder. It is in the shape of a tube closed at one end and tapped at the open end to receive the threads of the primer head. Several holes are drilled into the body to allow the flame from the primer charge to ignite the propellants The primer charge is contained in a foiling paper wrapping which lines the tube and prevents the powder from spilling out through the holes. The charge is sealed at the open end with a disc of onionskin paper.

The primer head has outside threads at the top for screwing into the cartridge case and at the bottom for threading into the body. The primer cup is press-fit into the head from the forward end so as to leave a portion of the cup exposed to the firing pin of the weapon. The primer cup contains a priming mixture weighing 1.2 grains sealed with a paper disc. The anvil is threaded into the head behind the primer cup. A beveled gas-check plug fits loosely into a cavity in the anvil. A plug with a flash vent machined into it, threads into the head behind the anvil.

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TM 9-1904, Ammunition Inspection Guide (1944)