I found this and the remainder can be found at the page at the bottom.
From roughly 1880 to 1930, there were several manufacturers and importers in this country that supplied double-barreled shotguns to anyone who would order them. They not only made them under their own name, but for dozens and dozens of hardware wholesalers, hardware stores, mail- order catalogs, sporting goods stores and many other retail and wholesale gun dealers, each engraved or stamped with their individual trade name or names. Add to this various grades, and suddenly there are vast numbers of essentially the same shotgun, all with different names engraved on them. Made largely with Damascus, twist or laminated-steel barrels, virtually none are safe to shoot as they are.
Damascus or twist-steel barrels are made by layering alternate strips of steel and iron then welding them together. The strips are then twisted until they resembled a screw, three of these wound strips are then welded together, wound around a steel mandrel, then welded and hammered into a barrel tube. Laminated steel barrels are a bit different. They start with a ball of steel and iron that is then hammered into long strips and twisted, then, like their Damascus cousin, wound around a mandrel, welded and hammered into a barrel tube. Inherently, these barrels are quite strong, and many best-quality Damascus barrels pass nitro proof. However, because of the iron content and welded manufacture, twist barrels have a propensity for rusting within the barrel material. Added to that is the fact that these guns were primarily used with non-corrosive priming, and are therefore potentially honeycombed with weak spots. While there are first-quality Damascus Parker and Purdey barrels that can be shot with modern ammunition, most if not all are not up to the task. Briley Manufacturing [(800) 331-5718] can either make full-length tubes of a smaller gauge--20 ga., 28 ga. and .410 bore in a 12 ga.; 28 ga. in an existing 16 ga., etc.--or, provided the barrels are good condition, install steel chamber sleeves of one gauge smaller--12 ga. in a 10 bore, etc.--enabling the use of smokeless-powder ammunition. Shooting these old hammer guns is real fun. Organizations like The Vintagers [(413) 339-5347] are devoted to shooting and keeping alive the tradition of these old guns through clay-target competitions. As much fun as shooting these guns is, safety is the prime consideration, and one should never, ever consider shooting a Damascus, twist or laminated-steel barreled shotgun without first having it inspected by a truly competent gunsmith, and, if necessary, altered by an outfit such as Briley.
http://www.briley.com/articles/grampas_shotgun.html