it gets unstable (not really the right word, its not like dynamite), due to hydroscopic action where it might get damp then dry out over and over.
To see if the rifle is loaded, take the ramrod and run it down the barrel. if it goes almost all the way down your good. I cant remember the length that would still be sticking out, but you can set the ramrod next to the barrel to get a rough measurement (compare it to the point where the percussion cap nipple enters the barrel