FWIW:
I get to 600 yards without a lot of trouble with a 308 and Leupold 3.5-10x40.
A precision barrel, a very good trigger, and a rigid high quality stock are necessary. Optics, are icing on the cake.
Heck, 300 meters, with a fixed 6x scope is pretty easy.
Remember, a 12x17 inch target with a 6x scope is like shooting a 72 x 102 inch target with a single power scope.
It ain't hard to see something that big (72 x 102 inc) at 500 yards.
Its quite hard to hold dead center on it though.
BMT