High Quality Content by WIKIPEDIA articles! The .357 S W Magnum (9x33mmR), or simply .357 Magnum, is a revolver cartridge created by Elmer Keith, Phillip B. Sharpe,Colonel D. B. Wesson of firearms manufacturer Smith Wesson, and Winchester. 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. The .357 Magnum cartridge has a positive reputation for stopping power.