xsheadspace,
That business with the set screws for adjustment is really a slick way to do it. I have contemplated doing something similar but was afraid the barrels might eventually shake apart if they weren't soldered clear down to the muzzles. Will you go ahead and solder it up tight after you get the barrels adjusted like you want them, or just leave it that way? This is the kind of innovative thinking that pushes us ahead of the oldtime gunmakers. There is no reason to have to do some of these things the old way, except "that that is the way they have always been done!"
I will admit that some of the old ways work out best in the long run, but we need to learn to seperate out the tried and true best methods from all the "traditional wisdom" B.S. that is floating around out there about doubles.
I have only done a few of them myself, but I have read up on construction methods, etc. quite extensively, and many things that get repeated as wisdom, or the Best Way, don't turn out to be true. Here's one for instance. How much have you heard about the old time gunmakers spending hours at a bench, reaming and straightening barrels by sighting down through them to be sure they were good and straight? Now, consider that most, if not all, double rifles have their barrels converging together to start with and then are slightly sprung apart or bent towards the muzzles. In other words, according to the "Oldtimers" , none of our doubles should shoot well at all because they all have bent barrels.
Some will say that that is an exception to the general rule and doesn't apply to any other guns. But that's wrong too. I can guarantee you that most double barrel shotgun barrels are bent ,also.
The companies back then did use different size frames for different weights of shotguns, but, amoung the same frame sizes, you will find both Upland game guns, Waterfowl guns, Skeet guns, And Trap guns. An Upland shotgun might have barrels that converge at 20 to 25 yards, a Skeet might converge sooner than that, a Trap gun will most likely be about like the old Waterfowl guns and converge at about 40 yards. How do you think they got them to converge at different distances using the same unaltered frames? Simply by bending the barrels slightly.
I recently read on here that a shotguns' chambers are situated at right angles to the standing breech face. Close, but not true. The chambers converge slightly together on all double shotguns that I have ever worked on. You can prove this to yourself when you get ready to bore out a monoblock. Keeping the monoblock lined up on the lathe, bore out one side, then do the other side, you will have to reset the vice to hold the other side in line because the bores converge slightly. This slight convergence was built in by the old shotgun makers and is a standing tribute to their forethought and inventiveness. The slight angled-in attitude did not hurt the shotgun shells for reloading, nor will it bother your rifle, but you may find that you have to go just a little deeper than you thought at first, to get the case heads down flush so the action will close completely. If you stop chamber reaming when the outside of the rim is first down flush, your gun won't close completely, because the inside edge of the rims are still protruding slightly, because of convergence in the monoblock. They didn't miss many "tricks" back then. As a matter of fact, I am amazed at how far advanced they were. Bob H.