I don't sort my brass, except buy caliber.

Here's the problem with your view, my view, Rob's view.
What you are trying to get, consistent volume, is admirable; but your method flawed.
Volume is volume and weight is weight, short of a possible corrosion they never meet. Unless you know the specific alloy used, and how tight the tollerances for ingredients. And you know how many machines in the lot of brass confess from, and what their SD is for diamensional variation.... If you did know those answers, you would also know that each lot is different, so the single answer you are asking about; wouldn't be a single answer. "Match" brass would be subject to the same production tolerances, although you would ASSume them to be less, but don't know; so possibly would need sorted as well.

Rob says buy quality brass and don't worry about it. He is a very good trigger man, so must be on to something. I say don't worry about it at all. I Pressure Test stuff all the time, so I must be on to something.

See the problem yet? If you want to know how much internal volume difference there is, measure it.

From the 50+ years worth of 308 headstamps I use and have Pressure Trace data on, it doesn't matter. I Pressure tested some of the "Oh no! That year LC Match brass is scary different". Again, couldn't find any significant pressure change. Is it possible it matters? Heavens yes! But Everytime I've tested The new magic bullets, or the brand difference, or the "known" brass; I just don't find what is claimed.