Does the ramrod have a threaded hole in the ferrule on the end? If so, and you could determine the thread pitch, you can get a "worm" that fits in there. You then use the ramrod as a "screwdriver" and screw the worm into the wadding securely, then pull it out. You can then "dig" out the old shot charge. There will be a wad also between the shot and the powder. After removing it you can "dig" out the old powder charge. You will almost certainly find that the old powder has attracted moisture and has rusted the breech area badly.
https://www.trackofthewolf.com/Search.aspx?search=worm Before doing any of this I would prop the gun with the muzzles up and pour a copious amount of WD-40 down onto the old charge. Leave it several days for the liquid to soak down into the powder, rendering it inert. You cannot be certain it is inert without doing so, and you are in harm's way as you stand in front of the muzzles trying to remove the charge. I have pulled charges without doing that, but I wasn't giving advice to someone else, it was me and me.
If you're thinking "It's 150 years old, it's harmless" I offer this as a side note to show how long black powder can remain viable, under perfect conditions ............. I have a friend who used to be a fanatical WBTS artifact collector. He used a Nautilus metal detector and once found a big cannonball several feet deep. Some time after getting it home he found that he could remove the "fuse", or whatever the part is that set off the explosion upon impact. He did so and found a goodly amount of grayish colored black powder therein. He removed it, and on a whim, loaded some into a flintlock rifle and fired it. It was a bit weak, in his opinion, but still usable some 120 + years after the late unpleasantness had ended.
SRH
