<P> The cartridge was designed by John Browning for Colt, but the most influential person in selecting the cartridge was Army Ordnance member Gen. John T. Thompson . After the poor performance of the Army's . 38 Long Colt pistols evidenced during the Philippine--American War (1899--1902), Thompson insisted on a more capable pistol cartridge . </P> <P> The . 45 ACP has 1.62 ml (25 grains H O) cartridge case capacity . </P> <P>. 45 ACP maximum C.I.P. cartridge dimensions . All sizes in millimeters (mm). </P> <P> The common rifling twist rate for this cartridge is 406 mm (1 in 16 in), 6 grooves, Ø lands = 11.23 mm, Ø grooves = 11.43 mm, land width = 3.73 mm and the primer type is large pistol . The cartridge headspaces on the mouth of the case at the L3 datum reference . </P>

What's the difference between 45 acp and 45 auto