The 6.8 SPC was designed for the military as a cartridge that landed between the 5.56mm NATO and the 7.62mm NATO to be used in the AR-15/M-4 platform. It loses very little magazine capacity versus the 5.56mm (25 vs. 30 rounds), but has better knockdown power without much more recoil.
This caliber works very well in short barreled rifles and is an easy conversion for an AR-15, requiring only a barrel, bolt, and magazine swap.
For someone looking for an AR-15 for hunting, this caliber is a logical choice, especially for recoil-sensitive shooters.
Starline brass is safe to use in both 6.8 SPC and 6.8 SPC II chambers.