If you are wanting to shoot those kinds of distances, change the bolt case out and move to a 6mm SST and step above 100 gr bullets.I've looked for Sierra 100grn TGK for a year now and still can't find them anywhere. But I normally shoot 100grn Nosler Partion's. Problem is that bullet is like 29-30 mil at 1360 and is already subsonic at like 12-1250 if I remember right from the ballistic chart I ran
Or better yet, the 6.5 SS or PRC