A wildcat cartridge, often shortened to wildcat, is a custom-made cartridge for which ammunition and/or firearms are not mass-produced. These cartridges are often created as experimental variants to optimize a certain ballistic performance characteristic (such as the power, size, or efficiency) of an existing commercial cartridge, or may merely be intended as novelty items.
Developing and using wildcat cartridges does not generally serve a purpose in military or law enforcement; it is more a hobby for serious sport shooting, hunting, gunsmithing and handloading enthusiasts, particularly in the United States.[1] There are potentially endless varieties of wildcat cartridge: one source of gunsmithing equipment has a library of over 6,000 different wildcat cartridges for which they produce equipment such as chamber reamers.[2]