Parent case- .30 Remington
Case type- Rimless, bottlenecked
Bullet diameter- 0.277 in (7.0 mm)
Neck diameter- 0.298 in (7.6 mm)
Shoulder diameter- 0.402 in (10.2 mm)
Base diameter- 0.421 in (10.7 mm)
Rim diameter- 0.422 in (10.7 mm)
Rim thickness- 0.049 in (1.2 mm)
Case length- 1.676 in (42.6 mm)
Overall length- 2.315 in (58.8 mm)
Ballistic performance
Bullet weight/type-115 gr (7.5 g) (7.45g)
Velocity- 2,625 ft/s (800 m/s)
Energy- 1,759 ft·lbf (2,385 J)
Test Barrel Length: 16 inches (406.4mm)
Basic Information
The 6.8mm SPC cartridge was designed to address the deficiencies of the terminal performance of the 5.56x45mm cartridge currently in service with the U.S. Armed Forces.[5] The cartridge was the result of the Enhanced Rifle Cartridge program. Participating in the program were U.S. Special Operations soldiers, as well as armorers and other technicians from the United States Army Marksmanship Unit.[6] The development of this cartridge is remarkable in that it was designed by actual shooters in the armed forces, instead of by industry professionals. The goal was to create a cartridge that would bridge the gap between 5.56mm and 7.62x51mm, something that would perform similarly to the Soviet bloc 7.62x39mm AK-47 cartridge.
The program started the design by using a .30 Remington case, which was modified in length to fit into magazines that would be accommodated by the magazine wells of the M16 family of rifles and carbines that are currently in service with the U.S. Armed Forces.[7]
In tests, it was determined that a 6.5mm projectile had the best accuracy, but a 7mm projectile had the best terminal performance. Further tests showed that a 6.8mm projectile was the best compromise between the two, providing accuracy, reliability and terminal performance up to 500 meters. The combination of the cartridge case, powder load, and projectile easily outperformed the 7.62x39mm cartridge, with the new cartridge proving to be about 200 feet per second faster.[8] The resulting cartridge was named the 6.8 Remington Special Purpose Cartridge due to the size of its projectile and the fact that it was based on the .30 Remington case.
In theory, the new cartridge only requires switching the barrel, bolt and magazine of a rifle chambered in 5.56mm, but almost all parts manufacturers sell complete upper receiver assemblies chambered for 6.8SPC along with individual parts. While it's somewhat more expensive, it makes converting an existing 5.56mm/.223 rifle to 6.8SPC take less than a minute without any tools being required. In contrast, considerable gunsmithing skill, tools, and time are required to detach the barrel from the upper receiver and the gas system. Reconnecting the new barrel is not trivial, either.
