Just for clarification (correct me if I'm wrong):
-The round he showed was, indeed, an AK round, and while it wasn't a ".308" it was a .30 caliber cartridge
-I've talked to an Ex-Marine sniper, and while I'm not sure how the updated ones shoot, the M107's (formerly M82's?) don't have much recoil, and that's about where it ends. I'm not sure how they shoot nowadays, but back in the day they'd shoot 2, maybe 3MOA.
-The 2430m kill taken by Cpl. Rob Furlong was with a McMillan Tac-50, which would kick the arse of a Barrett any day
-The US banned all export of .50 BMG products, more specifically Barrett, so there's not a very big chance you'll ever be able to get your hands on one.
-Rohann