Why can’t I shoot all your listed .45 Colt loads in my Colt SAA and replicas?

For one reason, the metal used in the old guns isn’t up to the standards of that used in modern firearms. Besides the metallurgy problems, the real factor is simply the design of the guns themselves. While a modern Colt SAA or replica may be made of better steel than their ancestors, they are not nearly as strong as a Ruger Blackhawk or Freedom Arms revolver, despite their physical resemblance. The Colt (and SAA replicas) have relatively small cylinders, compared to the Ruger and Freedom Arms revolvers. This means that there just isn’t as much steel surrounding each chamber, resulting in a weaker revolver. The .45 Colt has been an excellent and useful cartridge for well over 120 years without “magnumizing” it. Use the data shown for the respective revolvers; and if you really need .44 Magnum performance, buy a .44 Magnum.