Bet it’s a N. Beyer if it’s not a parts gun.
I wasn't going to jump in on this, but JD could be right. I have pictures of two Beyer guns, one a rifle and one a smooth bore that came from the same family. They were for sale on a table at a large antique gun show. They both have stock profiles very similar, almost identical to the posted gun, though with less drop. The patch boxes have sideplates like the one above, and similar incised carving behind the cheek rest, though there is some raised portion to the carving, as Beyer was known to do. Trigger guard on one is very close, the other, not so much. The smoothbore is percussion with octagonal to round barrel. The rifle is flintlock with full octagonal barrel. Neither has a side plate like the one above.
Unfortunately, when I got the chance to photograph the guns I was strictly forbidden to post them anywhere, with this forum specifically stated.
The person who owned them at the time sometimes posts here, and is well-known author of books about long rifles. I don't know who owns them now, but I was told by the person who had them for sale that they had been sold.