There's something about the .50 that stands out? No S proffesor, its freaking huge.

The thing is, comparing it to .556 is an extreme example of that age old question of a few heavy and accurate rounds at long range, or lots of little ones at closer distances. Two rounds, two jobs. If I were forced to choose I'd take an AR over a .50 Barret any day. The .308, in the middle, is probably your best choice in an M1A1 or an FN FAL. Hard to wrong with either weapon.
FQ13