The pressure spike experienced in Black Powder ignition is far less than that of smokeless. No one wants to say (including me) that it would be impossible to blow up your gun using Black Powder cartridges, but realistically the odds of causing damage due to over-pressure or a bad load are fraction of what smokeless loads are.
Are you rolling your own or using commercial ammo like Black Dawge?
45 Colt was originally a Black Powder cartridge. It is possible (but difficult) to actually cram 40gr of powder into a modern cartridge, but even the government cut that back to 30gr simply to make the guns easier to control back in the day.
I don't know what powder charge commercially available Black Powder 45 Colt cartridges are using, but I would guess it's probably the 30gr load or less. If you load your own, the sky is the limit regarding what bullet weight or load you use. From 20gr +filler and a round ball for Gallery Loads, to 40gr and a 235 RNFP for knocking down stampeding Buffalo.
One word of warning though: If you start shooting Black Powder cartridges out of your gun, you more than likely will become completely addicted and require years of re-hab to break the cycle. Personally, I believe that re-hab is for quitters.
