Gunplummer,
Yup, I've seen gobs of brazing and welds on gun parts. I've run into several forearm studs that were brazed back onto single shotgun barrels, by the so-called 'local auto mechanic', and I would not fire them, nor work on them. The problem is, if you work on one of these beasts, without replacing the barrel, and it burst after the fact, they can say you caused it, and sue, even though what you worked on wouldn't have had anything to do with it.
The wost gun I ever ran into, was a Winchester 37, that I was polishing for re-bluing. The breech face is a steel block, on these, that is welded to the U-shape formed steel frame, on both sides, and on this one, the polishing uncovered porosity in the factory welds. I had to grind out the bad, and run welds over both sides, then go through having it heat treated, to save the frame. The gun wasn't worth it, but it was a customers, and I got stuck with the fix. There's two versions of these, on how they're made, and the other has a round breech plug brazed into a formed frame. This 37, though, had to be the type with the welds down both sides.
I have built several parts back up with weld, then reshaped them, because the part was unavailable, and if it needed normalizing, hardening, and tempering, I did it. I try not to do that, if at all possible.