It is somewhat similar to a Brown Bess, but it appears to have had two fairly wide barrel bands. From what I can see of the markings on the wood and barrel, the band closest to the trigger was fairly wide, but narrower at the top and wider at the bottom. Google photos of a model 1795 Springfield or a 1816 Harpers Ferry musket and you will see what I mean:
It also appears to have had a drum nipple, gauging by the size of the hole in the barrel. Probably converted from flintlock to percussion. If the markings reveal the country of origin, you should be able to figure it out. Aren't puzzles fun!