The .357 Smith & Wesson Magnum, .357 S&W Magnum, .357 Magnum, or 9×33mmR as it is known in unofficial metric designation, is a smokeless powder cartridge with a .357-inch (9.07 mm) bullet diameter. It was created by Elmer Keith, Phillip B. Sharpe,[3] and Douglas B. Wesson[3][4] of firearms manufacturers Smith & Wesson and Winchester.[5][6]
It is based upon Smith & Wesson's earlier .38 Special cartridge. The .357 Magnum cartridge was introduced in 1934, and its use has since become widespread. This cartridge started the "Magnum era" of handgun ammunition.[7] The .357 Magnum cartridge is notable for its highly effective terminal ballistics.