This flexibility prompted a boom in the development of wildcat cartridges suitable for the Contender, such as the 7-30 Waters and .357 Herrett and the various TCU cartridges, most of which were commonly based on either the widely available .30-30 Winchester or .223 Remington cases. The largest factory caliber offered for the Contender was the .45-70, which, although a much larger case than the .308, is still feasible because of the relatively low cartridge pressures of the original black-powder round relative to the limits of the bolt face of the Contender receiver. Custom gunmakers have added to the selection, such as the J. D. Jones line of JDJ cartridges based on the .225 Winchester and .444 Marlin.
This adaptability led to a surge in the development of wildcat cartridges compatible with the Contender, such as the 7-30 Waters and .357 Herrett, along with various TCU cartridges, most of which were based on either the widely available .30-30 Winchester or .223 Remington cases. The largest factory caliber offered for the Contender was the .45-70, despite its larger case size compared to the .308, due to the relatively low cartridge pressures of the original black powder round relative to the bolt face limitations of the Contender receiver. Custom gunsmiths have expanded the selection, such as J.D. Jones' line of JDJ cartridges based on the .225 Winchester and .444 Marlin.