I think that this rifle may have been built by two different people. The inletting for the lock and buttplate, particularly the buttplate tang on the lock side, is pretty rough, but the sideplate and patchbox are much better and the carving looks to me like it was done by a more skilled hand. Apart from a little wobble on the upper wrist cause by the carving, the architecture is great, and the engraving doesn't look like a first-time effort, either.
Either builder learned fast, or it was started, perhaps as a precarve, by a beginner, and finished by someone with rather more experience. However it came about, though, I think the end result is very nice.