1868/70 question

[BillF]

Update- I am working on it:). For a retired guy I sure don't seem to have much time to get things done.
I think I tend to go with the nicotine, smoke or something from inside a building - not rust or oils. This is based on the final outcome below.
I tried Carlsr's suggestion of kroil but with 0000 bronze wool. It removed some but not by dissolving it. More of elbow grease
Then tried paint thinner and then acetone being careful to not get any on the wood. No go.
I have a bottle of Uline cleaner and grease remover and BAM, off it comes. All these attempts were on small areas but definitely the uline stuff does it. This is why I believe it is smoke related. The uline product is strong enough to soften old finishes so next step is to remove the barrel and action and go to work. More to come with pictures after I do that