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.303 British (7.7×56mmR) is a .311 inch calibre rifle and machine gun cartridge first developed in Britain as a blackpowder round put into service in December 1888 for the Lee-Metford rifle, later adapted to use cordite and then smokeless powder propellant. It was the standard British and Commonwealth military cartridge from 1889 until the 1950s when it was replaced by the 7.62x51mm NATO.
The measurement .303-inch (7.7 mm) is the nominal size of the bore measured between the lands which follows the older blackpowder nomenclature. Measured between the grooves, the nominal size of the bore is .311-inch (7.9 mm). Bores for many .303 military surplus rifles are often found ranging from around .309-inch (7.8 mm) up to .318-inch (8.1 mm). Recommended bullet diameter for standard .303 cartridges is .312-inch (7.9 mm).
This cartridge has seen much sporting use with surplus military rifles, especially in Australia, Canada, New Zealand and to a lesser extent, in the United States and South Africa. In Canada, it was found to be adequate for any game except the great bears. In Australia, it was common for military rifles to be re-barreled in .303/25 and .303/22. In South Africa .303 British Lee Enfield rifles captured by the Boers during the Boer War were sporterized and became popular with many hunters of non-dangerous game, being regarded as adequate for anything from the relatively small impala, to the massive eland and kudu.