303 British Ammo
The .303 British (designated as the 303 British by the C.I.P. and SAAMI or 7.7×56mmR, is a .303-inch (7.7 mm) calibre (with the bore diameter measured between the lands as is common practice in Europe) rimmed rifle cartridge first developed in Britain as a black-powder round put into service in December 1888 for the Lee–Metford rifle.
In 1891 the cartridge was adapted to use smokeless powder. It was the standard British and Commonwealth military cartridge from 1889 until the 1950s when it was replaced by the 7.62×51mm NATO.