Neither MIG (metallic inert gas) or stick- SMAW (shielded metal arc welding) are correct for repairing the barrel(s) on your Crescent double gun-- glad you knew that. But TIG (tungsten inert gas) is also not the right process, as the high heat input in the HAZ (heat affected zone) will cause the soft solder in the ribs to disolve, and causing even greater problems. And heat input when welding on any pipe or barrel can cause an "out of round" result, unless you use the right process and preparation.
Looks like your barrel shortening process came out OK, as judged by your detailed fotos.
