Loctite has a product - Loctite 620 - that is supposed to replace silver solder in many applications. On their website, they indicate that this product is used to bond shotgun barrels in monoblocks, forend hangers and rib hangers in NCP Products' Trap shotguns. I think this is what Mr. Searcy may be using. Supposedly, exposure to blueing salts at 300F has no deleterious effect upon the bond, and the bond strength is around 60% that of silver solder.

The Loctite 620 product is an anaerobic adhesive that cures in the absence of oxygen. Assembly of a barrel to a monoblock would be very simple, fast and inexpensive. Other products, such as epoxies, could be used to bond ribs to barrels very successfully. It might be something to consider in a double gun conversion project.