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.

The .30-30 Winchester cartridge was first marketed for the Winchester Model 1894 lever-action rifle in 1895. The .30-30, as it is most commonly known, along with the .25-35 Winchester, was offered that year as the United States' first small-bore sporting rifle cartridges designed for smokeless powder. Since its introduction, it has been utilized alongside the development of flatter shooting cartridges, most prominently those derived from designs subsidized by interest in military expenditures, yet the .30-30 has remained in widespread use almost entirely because of reliable effectiveness in civilian applications, proven by putting food on the table for millions of people within a practical range of hunting situations.