The .38 S&W Special cartridge was a lengthened version of the .38 Government cartridge then in use. Developed for Smith's new Military & Police revolver early versions of the revolver included the ".38 US Service Cartridge" designation as S&W was disinclined to stamp .38 Long Colt on their product.

The .38 Long Colt, like other cartridges whose roots go back to percussion conversions, initially used heel based bullets. Most of those old Colts had cylinders that were bored straight through. Lacking the "step" in the chamber those Spanish American war era Army issue revolvers will chamber a .357 magnum.