Good trigger and a real long range cartridge doesn't hurt.
6mmBR or 6BRX can have 100" less drop and 20" less drift than a 308 shooting 175 SMks at 1000yds.
6BRX mag and function test video- 95gr SMK with a BC of .480 doing 3180fps from a 22" barrel.
http://www.youtube.com/watch?v=je3ulQuG3S0