This was a plate test cartridge dating from around 1932 when the UK Design Department utilised a .450 Nitro case that was necked to .303in. the bullets were standard 174gr. .303 Mk. 1 W (Armor Piercing) although lighter bullets as well as aluminium were also used. This cartridge had no official designation and was designed to be fired from a pressure barrel (Design DD/E/1259) and in specially converted Pattern 14 rifles. The charge depended on the purpose of the test, as striking velocities could be adjusted to simulate the effect of the bullet at different ranges.