I run across this fairly often with estate sale guns and most particularly if they present as wall/mantel guns.
First, I try a quick determination of the period of the application. Usually guesswork. Try to get a chip off to see if it is clear, relatively clear, opaque or yellowed/collored.
Second, I note whether or not it was applied to the entire gun at the same time.
Third, if not (on the second) I begin to disassemble to determine if the metal work was done totally and independent of the wood. Here, it is important to note possible effects on screws and hardware as in the case of partially filling screw slots, threads and the like.
While apart, I will start with alcohol as noted above to test-strip an out of sight location if the surface treatment exists out of sight on the gun. As in beneath the forearm.
If it does not exist out of sight, I will pick an otherwise high wear, low visibility point like inside the lever on yours.
It can go on but I'm hooping you get the gist of my incremental and sequential manner in approaching this scenario.
Many times, I will end up determining that a fella had prepped the gun for rough-use with materials at hand or suggested by Popular Mechanics, American Rifleman and such. He just didn't do it very prettily.
So, the key points are:
Be aware of the effect of the goo when disassembling/reassembling.
Be aware of the effect of your chosen *stripper* on original finish.
Be aware of potentially heightened atmospheric induced rusting once stripped.
Note that what works on metal may be more aggressive than you want on the wood.
But really, and I can't stress this too highly, be sure to fully clean the screw slots prior to EVEN TRYING a screwdriver.
Todd.