.950 JDJ

The .950 JDJ is a large caliber rifle cartridge developed by J. D. Jones of SSK Industries.

Cartridge
Loaded .950 JDJ cartridges are approximately the length of an empty .50 BMG casing (i.e., 4 in), and are based on a 20×102mm case shortened and necked up to accept the .950 in bullet. Projectiles are custom-made and most commonly weigh 3600 gr which is 8.2 ounces or over half a pound.

Rifles
As its name implies, rifles chambered for the cartridge have a bore diameter of 0.950 in, which would normally classify them as Destructive Devices in the United States under the 1968 (1934) National Firearms Act. However, SSK sought and received a "Sporting Use Exception" to de-regulate the rifles, meaning they can be purchased like any other Title I rifle by a person over age 18 with no felonious criminal record. The rifles themselves, of which only a handful have been made, use McMillan stocks and extraordinarily thick Krieger barrels bearing an 18 lb muzzle brake. Overall, depending on options, the rifles weigh from 85 to 110 lb 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 abuse. The sheer size and weight of these weapons makes them impractical for hunting use, as they cannot be carried afield. Thus, they are largely "range queens"—rifles that are brought to the range for a fun time, but not usually used for hunting or other "more practical" uses. Additionally, the cost of owning and operating such a firearm is beyond most shooters; the rifles cost ~US$8,000, loaded cartridges are $40 each, and the individual lathe-turned bronze bullets are $10 apiece.

Ballistics
The cartridge propels its 3600 gr bullet at approximately 2200 ft/s. This yields a muzzle energy of 38685 ft.lbf and a momentum of 154.1 Newton-seconds, about the same as a 20x102mm Vulcan round. This kinetic energy would allow the .950 JDJ to pass through several body-armored humans. It is comparable to the original tank rounds of World War I in terms of ballistics.

By comparison, the 5.56×45mm NATO cartridge, used in the M16 rifle, produces between 1200 - 1300 ft.lbf, while the .308 Winchester, a favorite for hunters and medium-range police/military sniping, produces between 2000 - 3000 ft.lbf depending on the load used. The ballistics of the .950 JDJ is more similar to that of the 20mm autocannon round, which delivers approximately 39500 ft.lbf. The muzzle energy of the .950 JDJ is comparable to the kinetic energy of a 2800 lb automobile traveling at 20 mph.

In a 110 lb rifle, this will develop well over 200 ft.lbf of free recoil energy if an efficient muzzle brake is not used. This is far beyond the shoulder-firing capacity of nearly all humans, even without considering the difficulty of shouldering such a heavy rifle. Shooting is usually heavy "lead sled" or similar shooting rest, and the rifle is not held to the shoulder because of the severe recoil and possible injury. The rifle scope has significant eye relief to avoid injuring the ocular orbit.