no, the m-16/ar-15 fires a 5.56x45mm round.
http://www.snipercentral.com/223.htm that page has a lot of information about that round, but note that it is talking about the effectiveness of the round in SNIPING which is much longer range than most other shooting. the 7.62x51mm NATO round (http://www.snipercentral.com/308.htm) is used in the american m-60, as well as many other weapons. i am not sure, but i doubt that you can get "armor-piercing" rounds in 5.56 NATO or 7.62 NATO, though maybe in a larger 7.62 round (7.62x63mm == .30-06 springfield).
on the wound note, you make a good point. there were actually NATO talks about redesigning the standard NATO 5.56 round because as soon as it enters the body (impacts a soft obstruction) it breaks apart into many smaller pieces, creating a large definently lethal wound instead of a hole. now about the .44 caliber (handgun) round given its relatively small size (length) and shape, it actually stays together on impact. odds are it would simply create a hole and pass on through, cause when it hits hard things (metal backstop at range) it simply flattens out, whereas the longer rifle rounds mentioned earlier dissapate when they hit the same target. that is assuming that the handgun round is jacketed.
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