Per the mili-wiki site the ORIGINAL 45 Colt load in blackpowder was "from 28 to 40(!?!) grains of blackpowder" with a "230 to 255(?!?) grain lead bullet"...
Thereby, at least to me, leaving a whole lot of "wiggle room" for reloaders?
Cheers!
P.S. If I were loading the 45 Colt "Ruger ONLY" pistol loads with Magnum powders I would use Magnum primers: otherwise I fail to see any difference (and Winchester seems to agree)... Small pistol and rifle and their small magnum varieties seem, for the most part, to be interchangable once one has determined that the firearms involved will reliably set them off. Performance-wise, I don't see much (if any?) differences. NOTE: cci #34 & 47 (NATO grade military primers designed to avoid any "slam fires") may be the exceptions, but I have found them to work just fine in other applications as well (i.e., 300 WIN MAG & 338 LAPUA). If a specific handgun (most typically a semi-automatic OR a revolver with a modified hammer spring) has a history of light primer strikes, it is obviously a different story.