The .351 Winchester Self-Loading (8.9×34.9mmR in metric, A.K.A. .351 SL or .351 WSL) is a rifle cartridge manufactured by Winchester.
Winchester introduced the .351 WSL in the Winchester Model 1907 self-loading rifle as a replacement for the Winchester Model 1905 and the .35 WSL. The .351 WSL 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 version of the Thompson submachine gun was also made to fire .351 WSL in 1919, but was never produced commercially.
The energy of this cartridge approximates the modern .357 Magnum when fired from a rifle.