Understand that, even though doublegun barrels are not struck this way, it would be possible for the barrels to touch all the way from the breech to the muzzles yet still have considerable convergence built in, if they had a straight profile taper. Convergence is based upon the center-line of the bore of each barrel. The outer profile of the barrels are what touch, or do not. They are tapered on the outside, towards the muzzles ........thicker at the breech, thinner at the muzzle.
Note that I am not saying barrels are assembled with them touching together all the way, under the ribs. I'm just using the extreme example to illustrate the concept. I.e., take two disassembled shotgun barrels, hold them together so that they are touching at the muzzles and also at the breech. If they are tapered like all I've ever seen are, there will be convergence. The hard part is regulating the amount of convergence to match the lateral movement, in recoil, of the individual barrel being fired.
If it's hard to perceive this, draw a set of barrels on a piece of paper, with a straight edge, and see for yourself.
SRH
