The .950 JDJ (24.1×70mm) is a powerful large caliber rifle cartridge developed by American gunsmith and weapon designer J. D. Jones of SSK Industries.
Cartridge
.950 JDJ cases are approximately 70 mm in length, and are based on a 20×110mm case shortened and necked up to accept the bullet. Projectiles are custom-made and most commonly weigh which is 8.2 ounces or over half a pound.
Rifles
As its name implies, rifles chambered for the cartridge have a groove diameter of . SSK received a "Sporting Use Exception" to de-regulate the rifles. Thus, in the United States, they can be owned like any other Title I rifle by an American citizen at age 18. The rifles use McMillan Firearms stocks and extraordinarily thick Krieger barrels bearing an muzzle brake. Overall, depending on options, the rifles weigh from and are therefore only useful for shooting from a bench rest or heavy bipod. Despite the weight, recoil is significant and shooters must be sure to choose components (i.e., scopes and bipods) that can handle the force. The sheer size, weight, and power of these rifles make them rather impractical for hunting use. SSK only manufactured three of these rifles and as of 2014 no longer produces the ammunition.
Ballistics
The cartridge propels its bullet at approximately . This yields a muzzle energy of .
By comparison, the 5.56×45mm NATO cartridge, used in the M16 and M4 rifles, produces between , while the .308 Winchester, a favorite for hunters, police, and military snipers, produces between depending on the load used. Even the .50 BMG, which has a kinetic energy of around delivers less than half the energy. The ballistics of the .950 JDJ are more similar to that of the 20 mm autocannon round, which delivers approximately . The muzzle energy of the .950 JDJ is comparable to the kinetic energy of a automobile traveling at .
In a rifle, this will develop well over of free recoil energy. Shooting usually involves a heavy "lead sled" or similar shooting rest, and the rifle scope has significant eye relief to avoid injuring the ocular orbit.