|.401 Winchester Self-Loading|
|Place of origin||USA|
|Designer||Winchester Repeating Arms Company|
|Bullet diameter||.4065 in (Script error mm)|
|Neck diameter||.428 in (Script error mm)|
|Base diameter||.429 in (Script error mm)|
|Rim diameter||.457 in (Script error mm)|
|Rim thickness||0.05 in (Script error mm)|
|Case length||1.50 in (Script error mm)|
|Overall length||2.005 in (Script error mm)|
|Rifling twist||1 in 14|
|Primer type||Large rifle|
|Maximum pressure||37000 to 39000 PSI|
|200 gr (Script error g)||2,141 ft/s (Script error m/s)||2,037 ft·lbf (Script error J)|
|250 gr (Script error g)||1,875 ft/s (Script error m/s)||1,952 ft·lbf (Script error J)|
| Test barrel length: 20|
Source(s): Whelen, Townsend. The American Rifle. Century Co. 1918 p. 266
Winchester introduced the .401SL in the Winchester '10 self-loading rifle as a supplement to the Winchester '07 and the .351SL in their offering of hi-power, self-loading rifles. The only chambering available in the Winchester Model 1910, the .401SL was used by France, Russia, and American company security forces in the First World War.
The .401SL proved powerful enough for both deer and other large game at ranges under 150 yards. Both 200gr and 250gr bullet weights were offered by Winchester and other ammunition manufacturers as factory loadings. With extra available detachable magazines holding 4-rounds each, the Model '10, could provide lots of firepower for the big-game hunter. This feature helped promote the use of the .401SL on dangerous game such as moose and grizzly bear in spite of the lack of controlled expansion bullet designs, which doubtlessly would have improved game-taking performance and the subsequent reputation of the .401SL cartridge.
The .401 Winchester self-loading, for comparison, is comparable in "stopping power", to a .41 Remington magnum fired from a similar length barrel.