ORIGINAL: Red Lion
I agree with all you said except the hitting a man-size target with an M-16 at 500 yards, as most typical soldiers would not be able to do that and do not train for shooting at targets at that far of a range.
Marines have to qualify with the rifle, and 10 shots are from the prone position at a man sized siloutte at 500 yards. 20 shots from 300 yards (10 kneeling and 10 sitting) at a head and shoulder siloutte and 30 from 200 yards (10 sitting, 10 kneeling and 10 off hand) at a standard round bullseye.
As far as KP's friend the "expert", it doesn't take much to qualify as an expert marksman. I've seen recruits that have never touched a weapon in their lives qualify as "expert"...tell your buddy unless he qualified with a 240 or better, he is just average. A score of 250 is perfect (50 out of 50 in the 5 ring), and to be an "expert" all you need is a 220. Highest score Iwitnessed on any range was a 248.