I am not the one to say this, as there are many much wiser than I in this august group, however, it is my understanding that black powder, if kept dry, (and away from sources of ignition) is very stable. (unlike some smokeless powders.) The muzzle loaders that were loaded over a hundred years ago, and yet fired when someone decided to heat the breach to remove the plug are legend. (I saw the bullet hole in one workshop wall from just such an occurrence.) If this statement is incorrect, one of you who know better, please wade in with a more accurate observation.