The 375 JDJ was designed and developed by J.D. Jones, from SSK Industries as part of a series of handgun and metallic silhouette cartridges around 1978. The purpose of these cartridges was to give added range and power to the Thompson – Center Contender pistol for hunting as well as metallic silhouette shooting. The 375 JDJ is based on the 444 Marlin case necked to .375-inch. The first specimen was given to me by JD Jones during an SA hunt in 1991.