I got my great grandfathers rifle a few years back and had it hanging on the wall, a friend came over and asked if I had ever fired
it. I took it down and checked the barrel length and found out it was still loaded, so to be safe I pulled the ball and wad then dumped out the powder, installed a cap and set it off to remove to remove any left over powder (it went puff), It had been loaded for over 70 years or so. It had been keep in the closet at home for many years, The reat of the powder I loaded into a rifle case and it went boom.
I cleaned the old rifle up and at 75 yards it exploded a plastic milk jug