The 6mm ARC is a recently introduced cartridge from Hornady that was designed to maximize long range performance from an AR-15. According to Hornady, someone in the US military wanted a rifle with the range of 7.62mm NATO and the light weight of a conventional M16. The numbers provided by Hornady do show less drop and more energy past 300 meters than other AR-15 chamberings. I wonder, though, if civilian shooters will want to adopt the 6mm ARC. Compared to similar 6.5 and 6.8 millimeter cartridges that are already available, the ARC is less effective as a hunting round at typical ranges and compared to 5.56 NATO, the ARC offers less capacity and higher recoil at a much higher price for defensive applications. The one area where I could see 6mm ARC getting traction is in high power rifle competition but that's a small market.