5.56 can go either way just like any other caliber. I saw a "Combat" Engineer fall off a Hesco barrier, somehow switch his weapon to burst mid-fall and put 2 out of the 3 rounds into his thigh and calf, It looked about like this. I saw a few cases up close center mass shots and they we're more or less simliar what you would expect, sometimes no exit wound, sometimes a grapefruit. It's funny how bullets react in tissue depending on angle, clothing, and apparently lucky farts.
On the flip side I also saw a guy get hit inside a bongo truck by 3 rounds of 5.56 (after the windshield had been shot out) to the mid and upper torso from about 100-50 meters away (driving towards us) and he got out of his own free will and took a few steps before falling over a few feet away, then live at least the 1-2 hours it took us to turn him over to the Army. He looked like he had been shot with a .22, very small entry wound, no exit wound whatsoever.
IMO there is no caliber that will do ____ every time. You hear stories of people surviving .44 mags to the head and on the same token people getting shot in the stomach with a .22 and having the projectile come out of their armpit, tearing everything the whole way.