Wikipedia:

The Rifle, .303 Pattern 1914 (or P14) was a British service rifle of the First World War period. A bolt action weapon with an integral 5-round magazine, it was principally contract manufactured by companies in the United States. It served as a sniper rifle and as second line and reserve issue until being declared obsolete in 1947. The P14 was the successor to the P13 Enfield and the predecessor of the U.S. Rifle M1917 Enfield.
During the Boer War the British were faced with accurate long-range fire from the famous Mauser rifles, model 1893 and 1895, in 7×57mm caliber. This smaller, high-velocity round prompted the War Department to develop their own "magnum" round, the .276 Enfield, in 1910. An advanced new rifle using a modified Mauser-pattern action was built to fire it, the Pattern 1913 Enfield (P13); effective mass production was still some way off when World War I started, to say nothing of the logistical nightmare of introducing a new rifle cartridge in wartime, so nothing came of it.
Adapting the design to fire the standard .303 round led to the Rifle, .303 Pattern 1914 (P14), a design fed from a five-round internal magazine. With its prominent sight protection ears on the receiver, "dog-leg" bolt handle and "pot-belly" magazine, it was distinctive in appearance. The action was essentially a Mauser design with some Lee features and optimised for rapid fire, with the action cocking on closing, a feature highly valued by the British Army with its emphasis on riflemen highly trained for rapid fire, but less valued in other armies, such as the US or Germany, where cock-on-opening designs such as the M1903 Springfield and Mauser 98 were preferred. Cock-on-opening actions became more difficult to operate when heated by rapid fire as the effort to open the bolt had to overcome the striker spring to cock the action as well as unsticking the fired case from the chamber. The P14 was an advanced design for the time, and was said to be the most advanced service rifle of World War I.[1]