I very much agree that the critical wall thickness numbers are the end of the chamber, the forcing cone, and every inch out to 9", which is almost never reported by sellers. "MWT of .030" is (almost) meaningless.
As Joe said, there is no published consensus as to MWT at the above locations, probably because vintage doubles have barrel steel of different composition and tensile strength.
Which makes the CIP standards of limited help in that the numbers start for Category 1 “Standard Steel” (Non-alloy AISI 1045) with tensile strength 101,526-123,137 psi

But we can make our best recommendations based on measuring lots of presumed unmolested vintage barrels, and there are lots of numbers here
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=379803&page=3
http://parkerguns.org/forums/showthread.php?t=31791

This is an example of feathering; 67 mm hull on left and 65mm on right

[Linked Image from photos.smugmug.com]

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