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BallThe ball round was "Cartridge S.A. Ball 15mm Mark Iz" and was approved in October 1939 and shown in LoC Paragraph B.3738 dated August 1940. It was to Design DD/L/10004.
It had a very brief life and was shown as obsolete in List of Changes in August 1941. The round was mainly used for practice.
The bullet was boattailed with a mild steel core with lead/antimony tip filling in a gilding metal envelope. Weight was 1160 grains and the round had a velocity at 90 feet of 2,900 feet per second with a maximum mean pressure of 21 tsi.
Identification was by a purple primer annulus and the headstamp which included "IZ".
The Ball Mark I was shown as obsolete in August 1941.Ball Mark I headstamped "15MM Z"
Practice
"Cartridge S.A. Ball Practice 15mm P Mark Iz" was given this designation and submitted for approval in late 1939 but was never finally approved for service. the design was DD/L/10123.
It had a light aluminium cored bullet that was designed to match the armour piercing round to 500 yards but dificulty was experienced by Kynoch in matching the trajectories of the two rounds.
It was not finally approved for service as the Ordnance Board felt that there was little need for a practice ball round since the practice tracer round under development would fill the need. In the event, the practice tracer round was not approved either.
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