We have a few AR's, hunt with them off snowmachine & 4 wheeler; great with team slings. Caribou came through a few weeks back and I shot a bull with 6.8 spc; 4X32 acog ghost ring/red dot. I had snuck in on them, but they winded me took off and didn't stop till they were 6-7 hundred yards away, started feeding again. I lit off 5 quick shots at a bull that didn't have his butt facing me. Hit him 2nd and 4th shot. If I can kill a bou at 600 yards with that little 6.8; why the need for 300's? I figure I'd prefer that 338 lapua or 50 for long range. And I know I could kill a moose with that 6.8 within 300 yards.
In case you run into a Bear. ;^)