If you use the pyrodex, be sure to clean as soon as possible. To be safe, clean your gun twice, and check the gun every day to check for rust for a week or two.
It's interesting you say that, as I'd used Pyrodex for years on my Old Army and never had an issue -- only when I used real BP did I have to watch it closely as you say.
Sadly, I haven't shot much of either lately................. (Must remedy that...)
Old No7