Sannop, hunters saying the .223 is an excellent MILITARY round says more then you realize

What is the purpose of a soldier in combat? To hunt the enemy and remove him as a threat. What is the best way to remove a threat? To incapacitate it. Best way to do THAT is to kill it, baring that, wound it enough to make it unable to react. 7.62mm rounds tend to be very effective at that, ask anyone that's ever been hit by one. .223 rounds on the other hand, are NOT real effective at that, again, ask anyone that's been hit by one. I've talked with plenty of people who've caught either/or and some who've actually caught both types of rounds. All of them agree, they'd rather be hit by a 5.56 then a 7.62 if they had to do it again. It's smaller, faster, and tends to actually do less damage in the real world then a 7.62 does. Hell, my own father caught a 5.56mm in the chest when he was in the 101st Airborn in '63, it went in, took a slight turn, then went out his shoulder blade. Pissed him off, and he almost beat the idiot who shot him to death before they pulled him off of the guy. He was hit while in the air during a parachute jump using live ammo, and was so incapacitated that he was able to land, remove his pack, then beat the guy senseless. This is opposed to the guys who dropped in Nam and weren't able to do anything after catching a single 7.62x39mm standard AK47 round while in the air(yes, they actually parachuted into the jungles at first) except hit the ground and lay there, either screaming or passed out.
Baring certain 'kill zone' shots, the larger the slug, the more effective it is, period. Smaller diameter slugs, no matter what their velocities, tend to have less energy transfer to the human body. That's a fact, proven time and again in actual usage, unless they are specially made to fragment upon impact. And, for the record, FMJ(full metal jacket) ammunition is NOT designed to do that, and the 5.56mm round used by the US military is FMJ. They use it because it's less prone to cause jams(tips don't deform in the clip/feed) and it has a better chance of penetrating light armor(in theory..5.56 rounds tend to be too light for that at 100m).
Personally, when I hunted with my Hakim 8mm mauser, I used home made loads using soft lead tips instead of a fmj. Jamming wasn't a concern, since I only fired 1 round at a target and only fired at 1 target usually. And I've yet to see a deer wearing kevlar or riding in an APC

I did test the ammo against armor though, and at 100m, my soft lead hunting rounds penetrated 1" armor plate steel with ease, while 5.56mm and even M1 Garand and M14 rounds did not. Just in case I ever ran across some mutated deer driving APCs...and because I loved seeing the faces of people when my Hakim tore up those armor plates at the range