TB, you needed to keep reading in McIntosh's book: " . . . selected according to how little hand-work would be required FOR A FINISHED GUN OF PREDETERMINED WEIGHT." Mr. Smith wants a 12ga for upland hunting. If I look in my 1940 Shooter's Bible, I find that--assuming Smith wants a gun at the lighter end of the scale--he can get one, 26-28" barrels, right around 7 pounds. That "predetermined weight", based on Smith's order through his local dealer, is almost certainly going to end up with 4 weight barrels, to get him what he wants. If he later decides he wants a heavy waterfowler (without going to the Super Fox), 32" barrels weighing right around 8 pounds, he can get that too--but it'd be with #1 or maybe #2 barrels, to match that predetermined weight. And since we agree that the barrels are key to dealing with pressure, and since we also agree that a heavier gun will handle increased recoil better than a light gun . . . you buy your gun for the purpose in mind, and you use the loads that make the most sense for that gun and that purpose. You might well shoot those new Super-X loads in your waterfowler; you might not in your upland gun, especially if it came from the factory with 2 5/8" chambers. Especially if we're talking prior to WWII, there were still WAY more factory 12ga shells offered in 2 5/8" than 2 3/4".
As far as well-maintained shotguns being as tight as new after 100 years or more of use . . . Unless the same person has owned the gun for 100 years, or passed down detailed records of said gun's use, we don't have a clue why it's still tight as new. Might be it was never shot all that much. And if it's loose, although we can sometimes detect signs of abuse, we don't really know that either. How do we know that the gun isn't loose because of the loads shot in it? Seems to me the recoil party is in retreat there, because if it's recoil that causes wear, then more recoil than the gun was built to handle is going to shoot it loose. In fact, I think 3 or 4 people have already suggested that.
The problem with most vintage guns is this: what we know about them is anecdotal (only applies to that particular gun) and almost always incomplete. It's like the 10 year old car with 10,000 miles on the odometer, only driven back and forth to school by the little old lady teacher. Who maybe has a mechanic boyfriend who tampered with the odometer. But comparing a car to a vintage (pre-WWII or older) gun, with the car, you might well buy it from someone you know, who bought it new. FAR less likely with a vintage gun.
