Mar 26, 2009 · Another excellent question! Actually there are 3 "9mm" cartridges, 9x19 which is the std. 9mm Luger, 9x18 which is known as the Makarov pistol cartridge, and our 9x17 .380acp cartridge.
The 9×18mm Makarov (designated 9mm Makarov by the C.I.P. and often called 9×18mm PM) is a Soviet pistol and submachine gun cartridge. During the latter half of the 20th century it was a standard military pistol cartridge of the Soviet Union and the Eastern Bloc , analogous to the 9×19mm Parabellum in NATO and Western military use.