Lest we forget...
The "ace up the sleeve" of Pyrodex is that it is non-progressive fouling.
Translation: Once you've initially fouled the barrel (and cylinder, and arbor or cylinder pin) it does not get progressively worse, causing you to stop and swab the bore and remove hard fouling before you can no longer shove a PRB down the bore on rifles. I have personally put over 50 rounds through my Trade Rifle using RS and never even had to run so much as a cleaning patch down the bore. I've also been able to run as many as 10 cylinders of P though my Remmy before the cylinder begins to feel sticky. Can't do that with real BP, although I admit I prefer to shoot it over Pyrodex. No corrosion issues that I've seen, but I do a thorough cleaning the day of shooting, and if not, most certainly the next day.