I almost hate to ask, but what consideration was given to regulation of the barrels before soldering?
Stan presents an interesting question here. I seem to recall reading somewhere that the makers of vintage U.S. shotguns merely aligned their barrels by sighting through them to converge on some point at an average shooting range, and then did the joining. That sounds haphazard, but careful bore sighting with a rifle can get you pretty close to desired point of aim. I have no idea what the actual truth is when it comes to SxS shotgun barrel regulation. I have read a bit about the process for regulating double rifle barrels during manufacture. It sounds like that can be a tedious process of both load development and adding or removing spacers between the barrels to get them to converge at a set range. I don't think it's likely that U.S. double shotgun makers lavished that much attention on run of the mill production shotguns.
I believe it was in Michael McIntosh's A. H. Fox book that he said Fox employees test fired their shotguns on the roof of the Fox factory right in the city of Philadelphia. I don't recall if this test firing was a Proof test, or to check choke boring, regulation, or all of the above.
