First, while there were a Few Chambers cut for an undersize brass shell so the wad would not have tp be oversize, the vast majority of brass shells were made to fit a standard chamber, no difference at all in chamber dimensions.
Many early makers of guns if brass shells were specified bored their barrels over for the larger wads. Both the special shells & oversize wads were soon found to be un-necessary & fell by the wayside.
For a given thickness drawn brass is inherently stronger than turned brass. The turned brass shells may, or may not, have enough extra thickness to make them stronger than the drawn shells. All of my brass shell use has been with drawn shells. The oversize wads ti fit are Much, Much more economical than the turned cases.
Don't recall there being a problem in muzzle loader days & they used no case at all. Used an original I Hollis 12 gauge quite a bit with anywhere from 1 oz to 1Ľ oz with an equal volume of 2FG black. Back when I was shooting it the most DuPont black powder was about the only Kid on the Block. It was still made up in Wilmington Delaware as I recall.
I would not count on the case walls adding much if any strength to the chamber. As already pointed out Max pressure does occur In the Chamber area, it peaking some distance down the barrel is an Old Wives tale which should have been laid to rest at least a century ago. Te gunmakers new it for when they started building guns for smokeless they Beefed up the chamber walls, not the walls further down. Powder curve graphs drawn from tests run in the 1920's show it plainly. These have been posted here many times.
