[Unclenick]

As I just explained in a parallel thread, SAAMI only specs the exterior dimensions of the case and finished cartridge. What a manufacturer finds he needs to do to the inside ti make the brass handle pressure is up to him. Some make it all the same, some don't. Also you can harden brass and increase its tensile strength by working it more, so the number of forming steps can affect it. Hatcher mentions once having headstamp markings struck extra deep to increase head hardness to get cases that would withstand burst pressures so he could determine what those actually were.

The conundrum for most hand loaders is will my pet powder charge be affected by changing from a standard to a +P case. That depends on the volume inside the case under the bullet. In most instances the domestic brands are close enough in exterior dimensions that you can determine this just by weight difference. If a set of +P cases with the same brand headstamp are heavier than the standard cases you have, then they have less capacity and you should back your load down.