I experimented with 60 gr. Pyrodex .54 pellets rolled with a lubed bullet in my .50 percussion Sharps rifles. Looks like an original rd and handles well compared to a paper cartridge.
However, the erosive effect on the gas plate seemed to be enhanced compared to BP. It also had an odd chemical smell some find offensive.
The biggest issue with using BP in BPCRs is not the rifle clean up, which is easier that with a smokeless rifle, but the brass. If the brass is not cleaned, dried and tumbled ASAP after firing, it can deteriorate very quickly. That is the main objection people have towards BP use in BPCRs.
I also anneal after each firing after reading that shooters like Butch Ulscher and Mike Venturino do so. I do so before FL resizing as one of my Shiloh 45-70s (a Farmingdale) requires it for ease of chambering.