The .303 Lee-Enfield round, also known as the .303 British, is a rimmed rifle cartridge developed in Britain in the late 19th century. It was the standard British and Commonwealth military cartridge from its introduction in 1888 until the 1950s. The cartridge was designed for use in the Lee-Enfield series of rifles, which were the standard issue rifles for British and Commonwealth forces during World War I and World War II.

The .303 round typically consists of a bullet with a diameter of .311 inches (7.9 mm) and a weight of around 174-180 grains (11.3-11.7 grams), propelled by a charge of smokeless powder. The cartridge case is rimmed, which means that the base of the case is larger in diameter than the body, aiding in reliable extraction from bolt-action rifles.

In terms of performance, the .303 British round was well-regarded for its effectiveness and range during its time in service. It was used in various conflicts around the world and gained a reputation for its stopping power and reliability.