I've got a couple.
AR-10(T) in .308. 3/4 MOA or better (all day long) with Fed Gold Metal Match 168grn ammo. Still trying to bring that down to 1/2 as I think I can. I've got the Springfield Armory 4-14X56 with the .308/mil-dot reticule (sweeeeeeeet optics). Can't wait to move into the new house so I have a place to set my reloader!
Remington 700 PSS in 300 Rem Ultra Mag. I didn't like the stock so I put on a Choate Super Sniper (who names these things???). I still need to hit the range again for a couple days to dial it in. The optics are still unproven but the rifle will shoot ~3/4 MOA (5 shot groups) with me behind it and a cheap scope.
My Bull Barrel AR-15 is proven to (at least) 500 yards with 3" wide ground squirrels. Not once or twice but many times. It's much more difficult to determine the range than it is to make an almost perfect hit at that range. I'd use a rangefinder, but if I take my eye off the scope, I'm afraid I wouldn't reacquire the target. Shaw barrel, hooked buttstock, psg-1 style grip, Shephard 10X scope (unfortunately not calibrated for the .223

), free floated barrel, match ammo, etc.. But then again.... Ground squirrels are stupid and if I miss once, it's easy to walk the following round into place. They just stand there and watch.