Eightbore, I doubt Purdey would've honed many barrels to such a point that a gun is no longer in proof. As far as wall thickness goes, a gunsmith I know contacted the maker (I believe H&H) about one of their 2" guns he had in the shop. He measured the walls and found them something like .018, if I recall. H&H had the original specs on the gun. Turns out the thin walls were that way when they left the factory.
Further on those out of proof barrels . . . assuming wall thickness is still above the recommended minimum (which it may well be, even if the gun is out of proof because it's .010 or more over standard), an auction house would be foolish to trash the barrels in question, because the gun would likely pass reproof at the next size up. Guns sold as "stock and action" are often sold with the barrels, for that very reason--and may be a very good buy, if someone measures the barrel walls. It's just that such a gun can't be sold as a gun, because it's out of proof. Doesn't mean, however, that the barrels go straight to the dumpster.
