If I were you I'd stay with a 50cal, 45's are to hard to find stuff for. I have a 50cal ACCURA set up with a Leupold Ultimate Slam ML Scope using a 240gr XTP Mag, 105gr's of Pyro and a T7 Primer. I shoot about a 2" Group at 200yds with it. I Practice, Practice, Practice long range shots and have taken a few Deer out to 175+yds with complete pass throughs. But ALL of these shots were at Standing Still Broadside Feeding Deer and I knew the Distances. So there's nothing wrong with a 50Cal for long range shots.
(BP)