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Possibly due to the limited and specialised use of these rounds, there is no record of approval of any proof round in Lists of Changes or other official documentation. Two types were however in use in the U.K.
WW2 American Proof
During WW2 there was a requirement for a proof cartridge for the testing of the many thousands of American weapons taken into British service. This was filled by using the standard American proof cartridge, "High Pressure Test M1".
The case was originally a special heavy case but from 1941 the normal ball case was approved as an alternative.Both types were tinned for identification. A typical headstamp was "F A 42".
The bullet was a special flat based bullet weighing 174 grains.
The propellant charge was adjusted to give an average chamber pressure of 68,000 lbs psi.
Post war proof
When development of new .3 inch rounds for the Royal Armoured Corps took place in the 1950s a new proof round came into service.
"Cartridge S.A. Proof .30 inch" was not shown in Lists of Changes and the date of approval is not known.
The case was the normal ball case but copper washed for identification. It had a Berdan primer with a purple annulus and occasionally an additional purple stripe across the case head. Unusually for a proof round the cap was not ringed in.
The bullet was the standard 150 grain ball bullet.
The charge was about 52 grains of NRN.12 nitrocellulose to give a proof pressure of 26.5 tsi.
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