Jonty, what to do? Here's what I would do. With a plastic syringe pump something like Hoppe's #9 into that little hole and let stand for awhile, then drain it out. Then warm the barrels and pump some melted gun grease ( Rig or whatever) into the hole so as to completely fill the void between the barrels. Bobs your uncle. When you shoot the gun enough to get it hot you will notice a tiny grease slick alongside the rib where it is not fully soldered but so what, makes it easy to wipe the barrels. Forget about the barrels bursting, I've seen barrels with holes rusted thru that were still in use. If the metal surrounding the hole is sound everything is kosher. Think about ported barrels. As an aside, I believe if more people examined their guns ( as you've had the misfortune of doing ) they would find similar situations. Laying ribs requires a LOT of care to do it right. Give me a ribless gun or the single top rib ( a la Darne ) any day.
Nial
