bullet weight of ) and in headstamps. .276 Enfield .303 British cartridges, along with the Lee–Enfield rifle, were heavily criticized after the Second Boer War. Their heavy round-nosed bullets had low muzzle velocities and suffered compared to the 7×57mm rounds fired from the Mauser Model 1895. The high-velocity 7×57mm had a flatter trajectory and longer range that excelled on the open country of the South African plains. In 1910, work began on a long-range replacement cartridge, which emerged in 1912 as the .276 Enfield. The British also sought to replace the Lee–Enfield rifle with the Pattern 1913 Enfield rifle, based on the Mauser M98 bolt action design. Although the round had better ballistics, troop trials in 1913 revealed problems including excessive recoil, muzzle flash, barrel wear and overheating. Attempts were made to find a cooler-burning propellant, but further trials were halted in 1914 by the onset of World War I. As a result, the Lee–Enfield rifle was retained, and the .303 British cartridge (with the improved Mark VII loading) was kept in service. Mark VIIIz In 1938 the Mark VIIIz "streamline ammunition" round was approved to obtain greater range from the Vickers machine gun. The streamlined bullet was based on the 7.5×55mm Swiss GP11 projectiles and slightly longer and heavier than the Mk VII bullet at , the primary difference was the addition of a boat-tail at the end of the bullet and using of nitrocellulose smokeless powder as propellant in the case of the Mk VIIIz, giving a muzzle velocity of . As a result, the chamber pressure was higher, at , depending upon loading, compared to the of the Mark VII(z) round. The Mark VIIIz streamline ammunition had a maximum range of approximately . Mk VIIIz ammunition was described as being for "All suitably-sighted .303-inch small arms and machine guns" – rifles and Bren guns were proofed at – but caused significant bore erosion in weapons formerly using Mk VII ammunition, ascribed to the channelling effect of the boat-tail projectile. As a result, it was prohibited from general use with rifles and light machine guns except when low flash was important and in emergencies. As a consequence of the official prohibition, ordnance personnel reported that every man that could get his hands on Mk VIIIz ammunition promptly used it in his own rifle. Tracer, armour-piercing and incendiary Tracer and armour-piercing cartridges were introduced during 1915, with explosive Pomeroy