By my measurements, my estimate is that it may only contain a ball with no powder. Either way, I already put penetrating oil down the nipple and will also put it down the bore to kill the powder if there is any. I'm also putting a small coating of liquid rubber on the nipple to plug it.
Many of these guns have been found to be loaded and I know of a few that had multiple charges on top of each other. People do strange things when being shot at.
I'm going to keep it just as I found it