The Brownells Nitre Blueing salts are heated to around 600F which is over 200F above the melting point of most of the solders used in most sxs gun barrel assemblies. 60/40 solder melts well below 400F
http://www.brownells.com/aspx/ns/store/P...0BLUING%20SALTS

There will be nothing but separate parts left in the bluing tray if this is the case.