I was wondering the same thing myself, except I don't think many shotgun ribs are silver soldered. When silver bearing solder is used, I believe that is usually reserved for brazing the breech and barrel lump section. I've seen quite a few products advertised as bore cleaners that will remove lead and copper bullet jacket fouling, and have used some such as Shooters Choice and Mercury Quicksilver (solvent for outboard engines). But I have mainly used them for copper jacket fouling in high velocity rifles.
I found this video where a guy tests a number of popular bore cleaners for their ability to remove and dissolve lead.
https://www.youtube.com/watch?v=8_ud2M1gGlULong story short, Outers Foaming Bore Cleaner worked best followed by good old/new Hoppes No.9, which has been reformulated since most of us started shooting. Nitrobenzene in the old Hoppes is a suspected carcinogen. I hope nobody was using it for after shave even if the aroma was heavenly.
My real question is, who sloshes enough bore cleaner on the outside of shotgun barrels to ever compromise the rib solder joints? We are talking about cleaning the bores here, not total immersion in either bore solvent, or caustic hot bluing salts as Miller mentions, which will corrode and loosen shotgun ribs. If you keep your bore solvent inside the bore where it belongs, you shouldn't ever have to worry about loosening ribs. I just read another article by a gun scribe last week that claimed that immersion hot bluing salts will melt rib solder joints. The lowest melting point for tin-lead solder is 361 degrees F and hot bluing tanks typically run about 70 degrees lower. Most silver bearing solders have a much higher melting point.
