If you have access to a Rockler Woodworking I have used there Heavy Duty Stripper a number of times and it has always cut the finish, even on a couple of Brownings I did (one a .22 rf and anther and O/U).

Just be sure to follow the instructions, be sure to use two sets of rubber gloves (one a heavy set of chemical gloves) and use in a well ventilated area.

It ain't cheap but it works...

WBLDon