Unlike paint if solder drips or splatters on something of the wrong temperature it wont stick to it...
This is true, and you would be able to feel it on the surface. You would also be able to peel it off with a fingernail.
I saw that rust on the barrels. I have little doubt that it would be gone with a few minutes of rubbing with 0000 steel wool saturated with WD-40. I see no indication in these photos that severe rust has compromised the Damascus. I'm certainly not pronouncing these barrels safe to shoot without a close inspection. We need a lot more information such as the condition of the bores, and whether those shiny spots might indicate that deep pits were filled with solder, and dressed flush with the surface. No sense talking about wall thickness yet, when we don't know if the bores look like rotted sewer pipes.
