rate was , 5 grooves, groove depth land width . The trials took place in Britain, Ireland, Egypt and South Africa and at the end, the Chief Inspector of Small Arms recommended a number of changes, which resulted in a quantity of 6 improved Pattern 1913 rifles being manufactured between March and April 1914. The outbreak of World War I led to the abandonment of the effort to introduce a smaller calibre rimless cartridge for purely practical reasons. Adapting the design (with largely cosmetic alterations aside from chamber and extractor redesign) to fire the standard .303 British round led to the Pattern 14 Rifle (P'14), which was fed from a five-round internal magazine by five-round stripper clips. Effective mass production in Britain during World War I was impossible, and so the P'14 became a de facto afterthought. Thus, the SMLE remained the standard British rifle during World War I and beyond. Design The Pattern 1913 Enfield was mainly based on the Mauser line of bolt-action rifles. Engineering concepts found in the German Gewehr 98 and American M1903 Springfield service rifle bolt actions were combined with design features of the British Short Magazine Lee–Enfield Mk III service rifle. The design of the Pattern 1913 Enfield showed the emphasis on accurate, rapid fire emphasized by British Army training during this period. The adjustable flip-up aperture rear sight with a battle setting when folded down was an excellent design, allowing rapid and accurate sight acquisition, and was advanced for the period. The Mauser-type bolt had a low-profile bolt handle with an integral safety lug built into its base that locked in the receiver. The unusual 'dog-leg' shaped bolt handle has a low profile and places the bolt knob just rearwards of the trigger close to the firer's hand, again facilitating rapid cycling and fire. Like the Lee–Enfield, the safety falls under the firer's thumb and can be operated silently. The action was configured to be easily operable, even when heated by sustained rapid fire, with slick operation, cock-on-closing feature and positive camming action when opening or closing the bolt. The Pattern 1913 Enfield bolt locking lugs had a 4 degree helical angle with matching angles on the receiver lug seats (the technical term is interrupted threading). This means that final head space is not achieved until the bolt handle is turned down all the way. The Lee–Enfield rifle also featured helical locking surfaces.