I have a set of starrett anvil mics. Plus blade mitotoyos calibers. I don't really trust the calibers down to .0001. So only place to measure with the starretts is the rim itself. Or the belt.

Here's my thing. I bet it depends alot on brass brand too. In other words, if you had a pressure strain gauge. And lets say for both pieces of brass, you are reaching 70KPSI. But the webbing of brass A is stiffer. Brass B might show greater than .0005" expansion.

Just thinking outloud.