One note, it is "NOT" the heat of the hot salts bluing which damages the soft solder joint. It is a chemical reaction between the alkalie & the solder metal. Hot salts blues operate around 300°F which is below the re-melt tamp of the solders used. In fact you could place the bbls in an unheated salt bath & the same effect (but no bluing) would take place, just at a slightly slower rate. It will also attack aluminum ferociously. In fact in the model shop I formerly worked in we made some fuselages of nickel by machining an aluminum form which was then built up with nickel plate & the whole placed in an alkaline (Lye) bath & the aluminum eaten out leaving only the nickel remaining.
Cold rust on 1940 Ithaca 37R.
Gun shop assumed but did not know it was soldered:
