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 rimmed rifle cartridge. The .303 inch bore diameter is measured between rifling lands as is the common practice in Europe which follows the traditional black powder convention.
It was first manufactured in Britain as a stop-gap black powder round put into service in December 1888 for the Lee–Metford rifle. From 1891 the cartridge used smokeless powder which had been the intention from the outset, but the decision on which smokeless powder to adopt had been delayed. It was the standard British and Commonwealth military cartridge for rifles and machine guns from 1889 until the 1950s when it was replaced by the 7.62×51mm NATO.