My Choice the 45colt
I would opt for a Lee single stage press or turret. They are cheap and effective. When you start loading .45 colt the same bullets and primers will work in .45 acp; though I tend to shoot 200 gr LSWC in .45 ACP and 250gr in .45 colt. Even upper range .45 colt loads (900-1000fps) are easy to handle in the mountain gun. As you can see I prefer the round to square conversion grips. I own and load for several 4" .44 mag revolvers, but not in the mountain gun configuration. Since I shoot 95% self loaded ammo, availability of factory is a moot point; however as someone pointed out if you want to shoot .44 special you will be paying in the .45 colt factory ammo range anyway.