I'm not an expert, but I would say you have a real prize there! I can't say what its value might be, but in my opinion, with this rifle's fullstock and full-sized patchbox, but what appears to be an original percussion lock, I would suggest some time in the second quarter of the 19th century as its date of manufacture. I would call it a "trade rifle," likely from one of the several manufacturers in Pennsylvania who made plain, sturdy rifles of this general type for the western trade, both in flintlock and percussion. Native people originally from the east, who had been "removed" to the west, showed a decided preference for rifles over smoothbores. Many rifles of this general type went to Indians, but a great many white pioneers used them, also. I can see your rifle is missing the side plate and it has certainly seen some use over the course of its life, but it is generally pretty intact. So many of these, over time, have been reduced to relics.
There were gunmakers in the west, notably the Torreys in Texas and Phillip Creamer in the Illinois/Missouri area, who made rifles of this general description, but I think the majority of these rifles came from Pennsylvania.
Regarding the lock, I think GOLCHER and GOULCHER are just alternate spellings. They produced thousands of these locks, which were used for original construction as well as replacements. Yours looks like a pretty good fit in its mortise, leading me to believe it is original to the rifle. If it is a replacement, the gunsmith did an unusually good job of fitting it to the existing inlet.
I would ask that you find an old-fashioned magnifying glass, and examine the top flat of the barrel very carefully, under good light. That's where you are most likely to find the riflemaker's name. As stated previously, the name on the lock will most likely be just the lockmaker. Most rifle builders of that period used ready-made locks, just as they do now.
These are my preliminary thoughts. There are people here who know a lot more about this sort of thing than I do. I will look forward to reading their comments.
That one is a keeper!
Best regards,
Notchy Bob