If in doubt....DON'T.
It's not the heat that's the problem, it's the corrosive bluing salts.
The chemicals literally dissolve lead solder, which is what older shotguns barrels and ribs are joined with.
Drop an older gun in the bluing tank and the chemical attacks the solder.
Result is, the barrels and ribs come out separated and in pieces, or worse, when the gun is fired the everything flies apart.
If you're not 100% SURE about how your barrels are assembled, you best option is to have the barrels rust blued, which is a process that uses chemicals that don't attack solder.
This is rather expensive to HAVE done because it's all hand work.
