You can use standard velocity 45/70. No bear load stuff or other high pressure loads.I looked into one of those Sharps 45/70
Do your own research on recommended pressure limits to run.
Remington 405 spcl is common available, there may be 300+ gr loads too
Data I found suggests keeping pressure under or near 30,000 CUP, , anything rated for a Trapdoor rifle should be safe IMO
reloading resources show loads for older rifles,
It should say right on the barrel by the calibre marking if it is black powder only - if in doubt call Chiappa. Don't trust the internet.I don’t think you can fire smokeless ,I don’t have anyone to teach me how to reload