|.401 Winchester Self-Loading|
|Place of origin||USA|
|Designer||Winchester Repeating Arms Company|
|Bullet diameter||.4065 in (10.33 mm)|
|Neck diameter||.428 in (10.9 mm)|
|Base diameter||.429 in (10.9 mm)|
|Rim diameter||.457 in (11.6 mm)|
|Rim thickness||0.05 in (1.3 mm)|
|Case length||1.50 in (38 mm)|
|Overall length||2.005 in (50.9 mm)|
|Rifling twist||1 in 14|
|Primer type||Large rifle|
|Maximum pressure||37,000 to 39,000 PSI|
|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 1910 could provide substantial 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 SL is of similar size to the later .41 Remington Magnum; but the longer self-loading rifle cartridge produced a muzzle energy of 2,000 foot-pounds force (2,700 J) with a 200-grain (13 g) bullet, while the magnum revolver is cred with a muzzle energy of 790 foot-pounds force (1,070 J) with a 210-grain (14 g) bullet. The .41 Rem magnum revolver comparison is not entirely fitting, however, as in a carbine a cartridge will often product twice the muzzle energy over than when fired from a revolver barrel.
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