.303 British Overview The  .303 British is a .303-inch (7.7 mm) calibre. It was 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 for rifles and machine guns when it was replaced by the 7.62×51mm NATO. It is still in common use in civilian shooting and is also frequently seen in the hands of insurgencies around the world.   Stats Ammunition Type Damage Bullet Velocity (m/s) Barrier Penetration Armor Piercing 215gr Hollowpoint 19 520 1.6 4 MkXI Light Ball 10.3 1015 1.65 4 MkI Ball 13.3 815 3.65 4 MkVIIIZ Enhanced Ball 16.2 777 2.72 5 MkVIIY Incendiary Ball 16 754 4.2 5 WEX AP Ball 10.2 914 10.8 95 Note: Barrier penetration represents the rounds ability to go through walls and barriers. Armor piercing represents the rounds ability to penetrate body armor plates.