Re: unstable 308
2500 FPS in 12x should work ok. Try the 155 Palma or Lapua Scenars and that will probably pix ya up.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.