Last weekend I had a pertinent experience. Having (finally!) returned to CAS after a long hiatus, I was working my way through a match using a 100-round box of older 45 Colt handloads. In the second to last stage of the match, I made an unplanned move from smokeless to BP, apparently I’d “consolidated some loads from an 1860 Conversion into the box without realizing it. I finished the match, the last 20 rifle rounds, using BP. Although I’d done this with this rifle (Uberti 1873) before, it’s enough to say 45 Colt wouldn’t be my first choice for BP in a rifle. Too much blowback and fouling, noticeable even after the first ten rounds. I have friends who shoot whole matches of BP with no trouble, but as pointed out above they use the calibers Winchester offered, 44-40, 38-40, or 32-20.
BTW, sort your cartridges carefully and don’t swap from mild smokeless to full-house BP mid string. Even without the obvious safety concerns, it really breaks your concentration.