.351 Winchester Self-Loading

The .351 Winchester Self-Loading (also called .351SL or .351WSL) is an American rifle cartridge.

Winchester introduced the .351SL in the Winchester Model 1907 self-loading rifle as a replacement for the Winchester Model 1905 and the .35SL. The .351SL proved popular with police and security forces as the only chambering available in the model 1907, and was used by France in both World Wars. An experimental Thompson submachine gun was also made to fire .351SL in 1919, but was never produced commercially.

The .351SL is considered inadequate by modern firearm experts as a deer round, but is generally suitable for mountain lion, coyote, or similar medium-sized game, while being over-powerful and insufficiently accurate for varmints. It has had some popularity in the jungle, where its lack of long-range power or accuracy are less important. When first introduced however, many found the .351SL to be a good deer cartridge at ranges under 200 yards, at least in comparison to the many low-pressure cartridges of the black powder era.