BM,
The "seams" between the ribs and barrels are generally soft soldered with 60/40 tin/lead solder. Alternatively, they have been soldered or brazed using various higher melting temp mixtures containing either silver or bronze or both.
The barrels are simply pulled together to get the predetermined dimensional convergence (angled together) based on earlier shooting experience. Spacers are put inbetween the barrels at a few locations where the bailing wire will be used to bind the ribs and barrels together to prevent them from bending the barrels inward excessively when the bailing wire is twisted up tight. Then the whole mess is heated with a torch to solder everything together.
Here's the link to the web article.
http://www.picturetrail.com/sfx/album/view/18691676
