Well the 6.8 does have more energy than the 223 and a better selection of hunting bullets for game bigger than coyoyes so if your target is deer and larger then I'd say its a viable choice over the 223.
From a defense weapon stand point I refuse to accept the claims that its a better round for combat than the 223 "WITH PROPER BULLETS !!" If you reload I'd highly recoment that you try out a 6mm-223 , it offers the heavier bullets for bigger game yet allows light weight bullets for varmints ,it uses the same amout of powder as the 223 but the bore is alot bigger thus making it much more effecient in shorter barrels , and it'll run fine through your regular 223 mags.
I get the chance to "play" with some SEALs and Navy SWCC operators often and we have discussed at length what a good round choice would be for the average man in modern combat. Several of these guys have had the chance to use the 6.8 in combat and nobody I talked to was impressed with it enough to give up the increased rounds of the 223. They stated that if their is an increased energy that puts men down faster that its so insignificant that it varies from man to man.
I have let them run my 6mm-223 upper on their full auto lowers and they are all impressed at how well it feeds , the fact that round capacity is the same , little to no increased recoil and its effeciency in a short barrel where the 223 realy starts to loose its luster in in the short 10.5" barrels that alot of these guys cary , all wondered why this round was not adopted before the 6.8.
What is it your wanting your AR to do for you? The AR-15 is one of the best fighting weapons in the world and the 223 is more than capible of killing men for 0-600yds , WITH THE RIGHT BULLETS
