Re: Antique Muzzleloader
That is good info, but not enought to help identify the gun. Can you provide good clear pictures of the markings and both sides of the lock and breech areas, as well as pictures of the buttstock and muzzle area. An overall picture would be good, also.
FWIW, Mayence is the French name for Mainz; the use of that spelling on something made there might date it to the Napoleonic era c. 1800 when the area was under French control. I can't find that name for any location elsewhere.