I've killed dozens of deer and pigs with a 6.8 and a few of my hunting buddies use it almost exclusively on pigs. Mostly the very common 115gr Fusion ammo--penetrates pretty deeply and is very accurate--but also with the 90gr fusion/gold dot and the 120gr SST load as well. The SST is the most destructive but I had one gun that didn't shoot them great.
I think the 6.8 and 6.5 feel closer to a 30-30 in terms of killing power and speed. Definitely a step up from 5.56/223. Holes are bigger and animals die quicker.
Also killed deer with 223 using 62gr fusions and 64gr gold dots and 75 and 77gr Hornady and Sierra bullets and generic 55gr softnose bullets. They all did pretty much the same thing. Smaller holes, maybe a little bit longer time before the animal dropped.
