WELROD Mk.II & Mk.IIA .32 ACP. Cartridge.
Designed by John Browning and introduced in 1899. It was marketed in the U.S. when Colt turned out an automatic pocket pistol on another Browning patent in 1903 hence the designation A.C.P. (Automatic Colt Pistol). It is one of the most popular pistol cartridges ever developed. In Europe every company that made automatic pistols chambered the .32 ACP cartridges. In Europe, it is known as the 7.65mm Browning, while in the U.S. it is designated .32 Automatic or .32ACP.
For decades it has been the standard police chambering in Europe but has now in most European countries been replaced by the 9 mm. Luger round. The .32 ACP cartridge is produced by all major ammunition makers in a wide variety.
The cartridges case is semi-rimmed, strait walled (see illustration) and uses a .311-inch diameter bullet.
Illustration courtesy of Mike Haas.