I am a member of several sites that specialize in older guns, all muzzleloaders.
You need to be a member to post to them and membership is not always open. You can try to get in, if you cannot you can send me all of the details and some pictures, I will get you an answer.
Try
Muzzleloader Mailing List or
The Muzzleloader Message Hide .
The MLML has some of the foremost authorities on old firearms from throughout the world, but it can be hard to get in at times.
Let me know if I can help.
Alan