Yes it is true that a lot of modern guns are blacked/blued with hot salts but that doesn't make it right. Silver solder and Braze are unaffected by hot salts but how can you be sure the rib to barrels fit has no holes or even tiny pin hole, hot salts will get in everywhere, many guns have holes in behind the extractor allowing salts right in under the ribs you cannot be sure that all salts are flushed away and it only needs the tiniest amount left behind for the damage to begin. I have two Purdey barrels in my workshop and two William Powells The Purdey guns have just been done by someone with hot salts and are already showing signs of weeping white crystals. the Powell barrels were done some time ago both are rusting badly down the side of the ribs pitting the metal pretty much the same will be happening under the ribs, I often get fairly new guns made in Spain and Italy that have been finished in salts and the ribs have popped, a fair few Perazzi guns too. I was always taught never to use hot salts on barrels, that is just my view I am certainly not telling anyone what to do. I think it is a cost thing hot salts is cheap to do, rust blueing not so cheap but rust blueing done properly looks better and is much harder wearing.
