Finally. Homeless has struck upon the truth. Unknowingly. These guns were cheap guns, built to a price point. Thus, the cheap way to make such a double is to employ the monobloc method of joining barrels to a pre-machined breech section that includes lump, chambers, bites, etc. It's essentially the same process used in sleeving a good gun. The solder you see is a sloppy joint job. The knurled ring around the barrels was supposed to hide this plus a none-to-precise joint. SKB used the same process, and so did a range of others. As someone said, "who sleeves an Iver Johnson?" The answer is nobody.