8.6mm Blackout
8.6mm Blackout (8.6×43 mm), also sometimes referred to as 8.6 BLK, is a centerfire rifle cartridge developed by the firearms manufacturer Q, LLC. It utilizes a shortened case from the 6.5mm Creedmoor necked up to an 8.6 mm caliber (8.585 mm or 0.338 in diameter) projectile. 8.6 Blackout is designed for use in bolt-action rifles or as a caliber conversion for AR-10 style rifles. The 8.6 Blackout is designed for barrels using a 76 mm or 102 mm (1:3 in or 1:4 in) twist rate and bullet weights between  for supersonic loads and  for subsonic loads. The only required modification to convert an existing .308 Winchester-chambered rifle to 8.6mm Blackout is the replacement of the barrel. All other components of a standard AR-10 rifle are interchangeable. Modifications to the operating system such as the buffer, buffer spring and gas system may be made in order to optimize functionality of the firearm. 8.6 Blackout fits in standard, unmodified .308 Winchester or 6.5 Creedmoor magazines with no effect on capacity. See also 
 9×39mm
 .300 AAC Blackout
 .308 Winchester
 6.5 Creedmoor

References

Pistol and rifle cartridges
Subsonic rifle cartridges