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Armour Piercing
The initial design of .5 inch Vickers armour-piercing bullet was RD 1238B in 1924 and experimental rounds were produced with the headstamp "R/|\L 24 1238B". This went on to become the W Mark Iz and the design DD/L/1238B.."Cartridge S.A. Armour Piercing .5 inch W Mark Iz" was approved in July 1927 and shown in LoC paragraph A.3487 dated May 1928.The flat based bullet had a cupro-nickel clad steel envelope with a hardened steel core in a lead/antimony sleeve. It weighed 580 grains. The propellant charge was 130 grains of nitrocellulose and velocity was 2,540 feet per second.In August 1933 a Cordite loaded version was approved as "Cartridge S.A. Armour Piercing .5 inch W Mark I" to Design DD/L/6025 and shown in LoC Paragraph A.9599 dated March 1936. The propellant charge was 142 grains of Cordite 7-2 with a single wad.Both types had a green primer annulus and included the code letter "W I" in the headstamp. The NC loaded version also included the code "Z". Left: Experimental Armour Piercing headstamped "R/|\L 24 1238B"
Right "Cartridge S.A. Armour Piercing .5 inch W Mark Iz" headstamped "R/|\L 32 WIZ"
The proof requirement was that seven out of ten shots to penetrate 18mm of armour plate at 100 yards at a normal angle of attack and an additional seven out of ten to penetate 14mm of armour plate at the same distance at 20 degrees angle of attack.
Both W Mark I and W Mark Iz were shown as obsolete in August 1948
Semi Armour Piercing
The .5 Vickers armour piercing rounds did not see wide issue, most being manufactured before 1935, and increasing use was made of the semi armour piercing version. Apart from being much cheaper to manufacture, the Royal Navy found it to be as effective as the full armour piercing version.
A Cordite loaded version, "Cartridge S.A. Semi Armour Piercing .5 inch F Mark I" was approved but was not shown in List of Changes.Muzzle velocity was 2,470 feet per second and maximum mean pressure was 22 tsi.Both types had a green primer annulus and included the code letter "F I" in the headstamp. The NC loaded version also included the code "Z". Although not approved until 1938, rounds will be found headstamped as early as 1935. The Cordite loaded F Mark I is rarely seen.The proof requirement was that seven out of ten shots to penetrate 15mm of armour plate at 100 yards at a normal angle of attack.
The "Cartridge S.A. Semi Armour Piercing .5 inch F Mark Iz" was to Design DD/L/8652 and approved in July 1938 and shown in LoC Paragraph B.2837 dated September 1939. The bullet was similar to the W Mark I in all respects except the steel core was not of the same quality hardened steel.
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