Jim, Even without much carving, that's a nice looking rifle!
I'm curious what you use for your wood blackening?
As for circa 1790/1800 and later guns, I'm fairly convinced that at least a fair percentage of guns leaving the maker had some sort of light varnish or shelac finish on them, maybe put on over linseed oil or similar. This thought is from seeing patches of what looks like original finish in the protected areas of a lot of rifles.
Then again, at this late date, it's hard to say whats original, or added a hundred plus years ago...
John