.303 British

The .303 British or 7.7×56mmR, is a .303-inch calibre 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. Wikipedia
Rifling twist254 mm (1-10 in)
Bullet diameter7.92 mm (0.312 in)
Case length56.44 mm (2.222 in)
Case capacity3.64 cm3 (56.2 gr H2O)
Rim diameter13.72 mm (0.540 in)
Used byUnited Kingdom and many other countries
Overall length78.11 mm (3.075 in)