My AR10 with 20" barrel likes 168 Amax's and at its best is an 800 yard gun. Wind pushes it around quite a bit at that distance. On a calm day it will shoot 3" 3 shot groups at 600. Not sure what grain bullets you are shooting but I consider 168s a good minimum at 600 and 175 Sierra or 178 hornady would likely do a bit better. The 168 eldm has a high ballistic coefficient for the 168 class and does really wellMy AR10 I built is a .308 with a 20" barrel. I have a Vortex Viper PST II 5-25x50 FFP, MRAD
the trigger is a CMC 3.5 lb single stage
I generally use Nosler
The Bergara i want is the B-14 HMR either 6.5 Creedmoor OR a .300 Win Mag and ill buy either another Vortex, or go with a Leupold Mark 5HD... but truth be told, i love my Vortex... so ill probably get another.