Always choose a gun & ammo that you are comfortable with. If you aren't practiced with it, you can fail in an emergency. A good 44 will usually shoot better than a 45 without some tune up work & 44 ammo is easier to come by than 45. Once you get your gun, practice & get first hit speed with it & either caliber will work just fine. Mackay Sagebrush can fix you up with some very good ammo when you're ready.
