The 6.8mm Remington Special Purpose Cartridge (also called 6.8 SPC or 6.8x43mm), was built with the modern battlefield in mind. The 6.8 SPC round was developed at the request of SOCOM in response to shortcomings of standard ball 5.56mm ammunition against enemies without body armor and often under the influence of narcotics, dulling their sensitivity to pain.
The 6.8mm addresses the shortcomings of standard 5.56x45mm ammunition by creating larger wound cavities, resulting in more rapid blood loss and larger lethal hit zones. The larger, heavier bullets of 6.8 SPC ammunition are also less sensitive to barriers, making them relatively "barrier blind", which is particularly useful in urban settings. Although 6.8 SPC has a larger case diameter than 5.56x45mm, the ammuntion weight is similar. Thus, 6.8 SPC allows for performance similar to 7.62x51 (.308 Win), but with the ammunition capacities like 5.56x45mm (.223 Rem)!
While the 6.8 SPC fits into AR-compatible magazines, the increased cartridge diameter precludes the use of M27 (5.56x45mm) links. Machine Gun Armory has developed a new disintegrating link specifically for the 6.8 SPC round, to allow its use in belt-fed light machine guns (& self-loading rifles) across the world. These links, called M68, are made to the same exacting tolerances as M13 & M27 links, but sized for 6.8 SPC ammunition. M68 links also work for 7.62x39 ammunition, allowing the use of a disintegrating belt instead of RPD belts!
As a highly-effective, yet lightweight, round, 6.8 SPC is becoming extremely popular with civilian shooters, law enforcement, and militaries across the world as a near-perfect balance of stopping power and ammunition capacity.