designs after the Mauser 98 cocked as part of the opening stroke. The rifle has a characteristic "belly" due to a deeper magazine, allowing the rifle to hold six rounds of the US .30-06 cartridge in the magazine, and one in the chamber. The M1917 Enfield like the Mauser Gewehr 98 had no magazine cut-off mechanism, which when engaged permits the feeding and extraction of single cartridges only while keeping the cartridges in the magazine in reserve. In a manufacturing change from the Mauser 98 and the derivative Springfield, the bolt is not equipped with a third 'safety' lug. Instead, as on the earlier Model 1895 (Chilean) Mauser, the bolt handle recesses into a notch in the receiver, which serves as an emergency locking lug in the event of failure of the frontal locking lugs. This change saved machine time needed on the rifle bolt, cutting costs and improving production rates, and this alteration has since been adopted by many commercial bolt-action rifle designs for the same reasons. The unusual 'dog-leg' shaped bolt handle is low profile and places the bolt knob just rearwards of the trigger close to the firer's hand, facilitating rapid cycling and fire. Like the Lee–Enfield, P13 and P14, the safety falls under the firer's thumb and can be operated silently. The M1917 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 design probably used helical locking lugs to allow for chambering imperfect or dirty ammunition and that the closing cam action is distributed over the entire mating faces of both bolt and receiver lugs. This is one reason the bolt closure feels smooth. The angled lugs had no tendency to unwind with chamber pressure since the "angle of repose" of smooth, lubricated steel surfaces is approximately 8 degrees. One advantage was that when the bolt handle was turned up the lugs cleared each other immediately so full effort was applied to the extraction cam. The trigger had a mechanical interlock to prevent firing unless the bolt was fully locked. The location of the safety on the right rear of the receiver has also been copied by most sporting bolt-action rifles since, as it falls easily under the firer's thumb. The