Is the corrosiveness of Pyrodex Pellets harmful to the barrel if leaving them in, inbetween hunts (rather than firing it off)?

Unfired pellets only need to be "slightly"concerned with larger bore diameters that may find some moisture creep into the bore wall areas. In that case, eventual hang/misfire may occur... but no corrosion without the heat in short-term hunting use situations. Most-all bores have no such overbore concerns.... just thought I would mention the remote possibilities.

By-the-way....... do you wear glasses, contacs... etc.... andwere not wearing them when you typed?...lol

You should always discharge your muzzleloader between uses for safety. You're only dropping a couple quarters out of the bank for this addedsafety. Also, you can then be sure condensation or otherwise moisture will not have dampened your powder and caused you to have an ignition problem at the time of truth.

If you've fired the rifle during the day then clean it ... no matter what you're shooting for powder. If you load on a clean barrel and do not shoot during the day, you could leave the rifle loaded or in the case of an inline, push the powder and projectile out. As long as the barrel was clean and dry and you keep it that way, there should be little or no problem.