how long can I leave a 50 cal kentucky (loaded) without it rusting? I heard that plugging end of barrel and keeping moisture out prevents rust. Rifle has patched ball.

Also rifle is Pedersoli and cablellas lit says use Pyrodex R - 72 gr. I have pyrodex p and heard that I can use by reduce about 10%. What do u experts recommend as max load w patched ball?