The .303 British or 7.7x56mm is truly a legendary cartridge, first developed in the 1880s as a black powder round, it was converted to cordite in 1890's and then to smokeless propellant in 1910.
This is the round that assisted Britain win two world wars. The .303 British was first used in the Lee-Metford Rifle which replaced the Martini-Henry in 1888. It is however perhaps more widely known for having been used in the famous Lee Enfield No.4 MK.2 Rifle.
(Left: The 303 British)
Indeed the Lee-Enfield remained the standard rifle of the British army until it was replaced by the 7.62x51mm NATO in the 1950s. Today there are still hundreds of thousands of Lee Enfields chambering this round still in circulation around the world which are being used as both hunting and target rifles. That said it is very rare today for deer stalkers in the UK to have their rifles chambered in this calibre.
Although over the years there have been numerous variations of bullet weight and design typically the .303 will propel a 150 grain bullet at around 2,720 fps producing around 2465 ftlbs of energy at the muzzle.
Typical Ballistics: (150 grain bullet)
Muzzle Energy: 2465 ft/lbs
Muzzle Velocity: 2720 fps