Interesting piece. More and better photos will help a lot. What are the initials in cursive in the barrel to the left of the stamped in "Gilmore"? These will/should shed light on the maker. The "Gilmore/Penna. is most probably an owner, and definately has nothing to do with the maker. I've never seen the calibre stamped on the muzzle like that. Bet you Gilmore probably did it....he seems to have been "Punch Happy" with his dies! According to my records there was no H.M.Gilmore engaged in building flint longrifles. Could have been, but you can be almost 100% assured that Gilmore was not the maker....bet on an owner. John Gilmore operated in Texas in the 1870's-80's, and Jerome Gilmore operated in Louisiana in the 1850's-60's, but both of these were makers of percussion pieces, not flintlocks.
IMO it's definately a Southern piece, but I think I see more southwest Virginia in it than Tennessee. Possibly very eastern Tennessee or even possibly the very western tip of North Carolina. The buttplate suggests a N.C. piece, but we're splitting hairs here! All the same area, so what the heck! Whatcha take for it? (big grin)!.....hope you don't mess with it trying to clean/repair it! Is the barrel swamped? Almost looks like it in the full view photo, but can't tell for sure. Is it rifled or smooth? More photos, please! What you could very well have is a "Southern Blend" (kinda like mixing white likker and bonded likker togather...BIG GRIN). In other words, someone took a barrel off one piece, a buttplate off another, the Ketland lock (good locks in that time period), made a stock and put it all togather. It's a simple Southern piece....no patchbox or even a grease hole. TP should have more and better comments. He'll be along shortly, I bet.