With the 20" barrel on my LTR I get highest velocities with IMR-4895 when using 165gr bullets. I would use any of the usual go to .308 powders like Varget, Rl-15, TAC etc and pretty much any 165gr bullet. Find a combo that will give you the best accuracy and have at it. I have had success with Hornady A-maxs, SST's and the standard Interlocks. This season I used Speer 165gr SP and BTSP's and they performed as expected. Used on on 1/4'ng towards shot at 120yds it broke the near shoulder, traveled the length of the torso and found in the opposite side hip. Weighed in at 135grs, no jacket separation and a perfect mushroom.