i see a lot of ruined blackpowder guns. Most of the guns i see in pawnshops have ruined bores.
Whether the shooter uses blackpowder or a substitute; the gun must be promptly cleaned soon after shooting. A friend ruined his expensive Knight disc rifle when he left it uncleaned for nearly a year. Pyrodex is as corrosive as black powder, perhaps more so. If left uncleaned a gun fired with Blackhorn 209 can rust.