"I'd be surprised to think that the industrial attachment of barrels and ribs would involve only one type of soft (hard, insert whatever choice you want) solder or brazing compound. Putting so many parts together, one after the other, must involve a discriminate selection of various glues that melt in decreasing order of temperature so that the first two parts attached don't get unglued on the last bit of bonding. Thus, stick-on the locking lugs with the highest strength stuff, then spot the ends of the barrels together, then move on to the ribs, and so on and hopefully the lugs won't fall off in the process. It's not easy and it takes immense skill and expertise while the tasteful results look effortless."
Typically, the barrels are joined at the breach end by brazing, for both chopper lump and dovetailed lump. Then, the barrel tube area is heavily tinned. The ribs are fitted and "wired and wedged" into place while the whole assembly is heated sufficently to flow the tin and join all parts together. With this process, regulation can be done by remelting the tin and shifting the barrels slightly. Brazed barrels require the whole barrel/rib/lump assembly be held in a jig and joined in one fell swoop. It is either right or not and remelt adjustment is not an option.
