The .357 Magnum is a revolver cartridge with a .357-inch (9.07 mm) bullet diameter, created by Elmer Keith, Phillip B. Sharpe, and Colonel D. B. Wesson of Winchester Repeating Arms Company in 1934. It is based upon Smith & Wesson's earlier .38 Special cartridge. The Buy 357 Magnum Ammo cartridge was introduced in 1934, and its use has since become widespread.