Mete is exactly right!
When I was doing restoration work for various museums back in the 70s we got in guns from the Civil War period (and sometimes earlier) on a regular basis.
I'd say about 1 out of 3 was loaded.
That makes sense if you think that in times when muzzleloading arms were the "assault rifles", you didn't wait until danger appeared before you loaded them. They were kept loaded.
Anyway, every loaded rifle or smoothbore I ever took apart had powder that was fully able to fire.
None of the charges were "dead". Not one!