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The first British use of .45 inch ACP occurred in WWI when the Admiralty purchased a number of Colt Government Model pistols in that calibre. It is believed that the army also purchased these pistols but the shipping records from Colt to their British agents The London Arnoury Company are not clear as to which were for government orders and which for private purchase.
WWI issue
"Cartridge S.A. Pistol .45 inch Colt Automatic" was not shown in Lists of Changes but is shown in the Vocabulary of Priced Stores.
The case was the normal .45 inch ACP case and those seen had a headstamp of "W 17". Some cases had a purple primer annulus.
The round nosed bullet had a cupro-nickel envelope and a lead core and weighed 230 grains.
The propellant charge was about 5 grains of Bullseye No.2 powder.
Muzzle velocity was 850 fps.
Above; Winchester round and headstamp. Right: Royal Navy .45 inch ACP Bundle.
WWII issue
In early WW2 Britain ordered large numbers of Thompson sub-machine guns together with many millions of rounds of ammunition from the United States.
The first order was for 3 million rounds from Remington in February 1940 followed by an order to Winchester western for 219 million rounds in May and June 1940. These rounds had the manufacturers normal commercial headstamp. Following the enactment of the Lend Lease Act in May 1941 Britain received large quantities of American military .45 inch ACP with regular U.S. military headstamps. Britain depended entirely on U.S. supplies of ball ammunition during WWII.
Ball Mark Iz
"Cartridges S.A. Ball .45 inch Mark Iz" was the British designation for the U.S. "Cartridge Calibre .45 inch Ball M.1911".
The case was the normal .45 inch ACP case with Boxer primer and made of brass or steel. Eralt British purchases were brass and were headstamped typically "REM-UMC 45AC" or "WRA Co. 45AC". Later U.S. military cases were either brass or steel and had regular military headstamps.
The bullet normally had a gilding metal envelope, sometimes tinned, with a lead core and weighed 230 grains.
The propellant charge was about 5 grains of smokeless powder.
Muzzle velocity was 850 fps.
British contract box by Western showing Lot 1 of 1940
Winchester British contract box
In 1943 Australia commenced manufacture of the .45 inch ball mark I at their Footscray No.2 factory. Post WWII the Australian Royal Navy kept the Thompson in service and manufacture of the ammunition continued until at least 1956. A typical headstamp is "MG 43 .45 IZ"
Australian .45 inch packet label
Ball Mark IIz
"Cartridge S.A. Ball .45 inch Mark IIz" was approved to design DD/L/14035 and 14036 in February 1943 for naval service. Despite this the round was not manufactured and did not enter service. It was shown as obsolete in Lists of Changes dated July 1948.
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