Springfield M1A! Americas gun.
.308 BTW is very common for Snipers as is .300 Hornady.
I have one of the 16 inch M1As and it is horrible. I've tried several types of ammo and they all suck. Maybe 18 inches is as short as you want to go. I sent it back to the factory and they recrowned the barrel and sent back a target they shot with Federal Match that was still 3 inches at 100 yds. If you use cheap ammo it practically patterns at 100 yds. Pretty disappointing.