The .454 Casull is a firearm cartridge, developed as a wildcat cartridge in 1958 by Dick Casull, Duane Marsh and Jack Fullmer. It was announced in November 1959 by Guns & Ammo magazine. The design is a lengthened and structurally improved .45 Colt case. The wildcat cartridge went mainstream when Freedom Arms brought a single action five-shot revolver chambered in .454 Casull to the retail firearms market in 1983. Ruger followed in 1997, chambering its Super Redhawk in this caliber. Taurus followed with the Raging Bull model in 1998 and the Taurus Raging Judge Magnum in 2010. The .45 Schofield and .45 Colt cartridges can fit into the .454's chambers, but not the other way around because of the lengthened case.

A wildcat cartridge, often shortened to wildcat, is a custom cartridge for which ammunition and/or firearms are not mass-produced. These cartridges are often created in order to optimize a certain performance characteristic of an existing commercial cartridge, or may merely be intended as novelty items.