RE: How long will powder stay good?
Blackpowder will still be good years and years from now if it's kept dry! I have read of instances where old muzzleloaders were found in attics, etc. where they had been stored for years and they still had a load in them that was good. I'm certainly not suggesting anyone should try firing any gun in that condition because there are obviously other considerations to take into account, I'm just relating what I've read!