Except that the military doesn't really care how quickly or humanely the guy dies, or really if he dies at all. A dead man reduces the force by one, a wounded man reduces it by two. In fact, while the M855 5.56mm NATO green tip ball round is rated to a max effective range of 550 meters against a point target (i.e. a single man), the reality is that it's highly unlikely that individual infantrymen armed with service rifles would ever engage the enemy at such range. At that range you're far better off calling for arty or an air strike. In leu of arty/air support, your next best option is using medium and heavy machine guns (the M240G 7.62 x 51mm and M2 .50BMG, respectively).

We're talking about HUNTING, which is a whole different ball game. When hunting it is an ethical imperative to make every effort to ensure that the animals we take are harvested in the quickest and most humane way possible. Part of that is selecting an appropriate cartridge, bullet and max range to shoot at. The .223/5.56 (which are very similar, with only small differences in case thickness, chamber design and, in the case of military ammo, max pressure levels) is really running out of steam by 500 yards. It's just not carrying enough energy at that range to perform like it should against an animal target. At ranges past 300 yards, the .243 Win, 6mm Rem and .25-06 are all great choices for flat shooting rounds that carry much more energy than the .223 at 500 yards, and have higher BC's across the board to boot (a definite advantage past 300 yards).

Mike