I said this before on another thread, but I would find the smith first. Once you decide on a caliber, find a gunsmith from this site to build this gun for you. Fifty said that it's easier to tell him what you want, such as a barrel and stock, then let him order it. As for caliber I would go with the straight .338 Lapua, it seems like it will what you want. That said, any of the other suggestions here would also do the job.