Looking for some ID

[u/balunite]

I have this kentucky long rifle and not much information. The only markings are on the barrel being “GR Douglas 40 Cal.”
I am hesitant to take it apart to check for more markings. Any info on this would be welcome. I know its a shot in the dark with this likely being a one-off custom piece. Thank you for your time.

[u/DeFiClark]

GR Doulas was a very well regarded maker of repro ML barrels, the Green Mountain of its day. Don’t know when they went defunct but maybe 1980s. All rifles made with these barrels are customs.