.303

The .303 British (Also known as 7.7mmx56R) is a rifle/machine gun round.

History
The .303 round was adopted by British forces in the late 1880s, originally as a black-powder cartridge. Later technological improvements revised the round first to a Mark 2 configuration using cordite, then finally to smokeless powder in later marks. While generally issued as military ball ammunition (a solid bullet), some Mark 5 and Mark 6 rounds were designed as hollow-point expanding rounds before international treaties forced their withdrawal.

This round remained the British Army's primary rifle cartridge until the mid-1950s, when it was phased out in favor of the NATO standard 7.62x51mm round.

Design
Unlike many modern brass-jacketed rifle cartridges, the British .303 employs a rimmed cartridge, which forced certain design compromises in magazines and extractors for weapons that employed the round. Generally, militaries preferred rimless cartridges that could be more easily loaded and enjoyed a more efficient magazine configuration. The .303 was among the last rimmed military cartridges manufactured.

Despite common misconception, the .303 round is not 0.303 inches in diameter, but is instead 0.311 inches across its nominal width. The .303 name is the nominal measurement between rifling lands within the bore of a weapon designed for this cartridge. The round swages, or rams and engages the rifling, imparting spin and stability to the bullet.

With case, a .303 bullet stands 2.22 inches tall.

Bullet weight varied by design, from the lightest high-velocity round at 9.7g, to the heaviest, slow-moving, hard-hitting 12g round.

Performance
The weight and amount of propellant that make up the .303 cartridge lend themselves quite well to making a high-powered rifle cartridge. Weapons employing the .303 round are generally noted for good penetration and accuracy characteristics.