If I remember right, it's the tin(?) in the lead/tin soft solder that is effected by the caustic soda of the hot bluing soln.
The tin/lead alloy bond of the solder is weakened. That is the problem
Anyway, look at the bores of the bbls. They will be blued too including the chambers. Sometimes you have to look a bit sideways at the bbl wall to see the bluing. A glance straight doown the pipe will only show it to be nice and shiny as a polished surface would,,blued or unblued.
Locking bolt surfaces and small undercuts and such on the lugs,,everything gets blued in hot blue immersion.
To bring them back to some look of a rust blue they'd all have to be carefully repolished. Not something easily or normally done by the HB guy. Nore would they normally repolish the bores and chambers to an in the white look.
An older set of bbl should have the patina, darkened discoloration to the in the white areas, but in the white none the less.
I worked w/a gunsmith many years ago that used to add a magic measured amt of potasium cyanide to his home brew hot blue soln.
That was to allow soft solder assembly bbl sets to be hot blued.
I had read where that supposedly supressed the soln from effecting the solder.
He swore by it, I remember a few still coming apart in later years,,, and it didn't do the big yellow barn cat any good that used to wander the shop after she walked through the bluing room one day.
