The .223 / 5.56mm was primarily designed to humiliate the person being shot. The 6.8 was designed to kill, even if it doesn't hit the intended target. Even though they both use the same lowers, you can clearly see that the 6.8 Remington Special Purpose Cartridge is a superior round.
As they say, a picture is worth a thousand words*
*And of course, Photoshop's worth about $500 bucks...