.401 Winchester Self-Loading

The .401 Winchester Self-Loading (also called .401SL or .401WSL) is an American rifle cartridge.

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.