Are you serious?
The 6mm's and 6.5's have much better BC's. Combine that with at least as much muzzle velocity as the .308, and often more, and there's less wind-drift--which is a larger factor than 100-yard groups as the range increases.
All I pointed out is that it's easier to build better-balanced bullets in larger calibers than smaller calibers. When diameter gets down to .224 it's tougher than with 6mm and 6.5mm.
