I recently bought a 12 ga. fox sterlingworth with untouched screws and and a very tight action. Unfortunately, or fortunately, someone since 1917 has coated the barrels and action with varnish. Under this aging brown mess, the barrel blue seems to be very well preserved. Can anyone tell me what the best way to get this stuff off without damaging the blueing? I have tried gunscrubber, nail polish remover, and acetone with little to no success.

Thanks,
Tom