The .950 JDJ cartridge is a large-bore rifle cartridge developed by J.D. Jones of SSK Industries. Jones is also the noted developer of many other well-known cartridges, such as the Whisper family.
The .950 JDJ is among the world's most-powerful, and largest-caliber, rifle cartridges. Loaded .950 JDJ cartridges are approximately the length of an empty .50 BMG casing (i.e., 4"), and are based on a 20mm Vulcan case shortened and necked down to accept the .950" bullet.Projectiles are custom-made and most commonly weigh 3,600 grains (8.2 ounces, or over half a pound).
As its name implies, rifles chambered for the cartridge have a bore diameter of 0.950", which would normally classify them as Destructive Devices under the 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 (8.2 kg) muzzle brake. Overall, depending on options, the rifles weigh between 80 and 110 pounds 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, though impressive, 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.
The .950 JDJ has become something of an internet legend, and is frequently cited as an example of a "ridiculously large" cartridge, thanks to its overwhelming ballistic figures. The cartridge drives its aforementioned 3,600 gr (230 g) bullet at approximately 2,200 ft/s (670 m/s). This yields a muzzle energy of 38,685 ft·lbf (52,450 J). For comparison, the 5.56x45 cartridge, used in the M16 rifle, produces approximately 1,200–1,300 ft·lbf. The .308 Winchester, a favorite for hunters and medium-range police/military sniping, produces between 2,000 and 3,000 ft·lbf (4,100 J) depending on the load used. The .950 JDJ produces a colossal amount of energy by comparison. In a 110 lb (50 kg) rifle, this will develop well over 200 ft·lbf (270 J) 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 should be done with a heavy "lead sled" or similar shooting rest, and the rifle should not be held to the shoulder unless the shooter is prepared for severe recoil and possible injury. The rifle scope should have significant eye relief to avoid injuring the ocular orbit.