https://en.wikipedia.org/wiki/.357_Magnum
The .357 Magnum cartridge is based upon Smith & Wesson's earlier .38 Special cartridge. It was introduced in 1935, and its use has since become widespread. This cartridge began the " Magnum era" of handgun ammunition. [6] The "Magnum era" began with the .375 H&H rifle cartridge, spreading to handguns with the .357 Magnum.