I know that mil brass is thicker, thus there is less case capacity. Being thicker does it expand less therefore requiring less powder to produce equal pressure?

Perry

They are able to withstand stretching better when fired in loose chambered military weapons (done for reliability purposes). There is a pressure specification difference also .
heavier cases and reduced volume. the nato cases are slightly diffrent in dimention than the 308 win. I would reduce the loads and fire form the military brass.
I tried loading some 308's mil. brass at near max and shot it in a military rifle chambered for 7.62x51 or .308 and the cases were stretvhed and hard to resize ,,no real pressure signs.
Tried the same load in a rifle chambered in 308 win. and had really hi pressure signs. extractor marks and pierced primer.
Follow the rule reduce by at least 10% and work up. some loads with imr 4064 showed hi-pressure even at the lower loads.
Dave

Perry I have used quite a bit of military brass in 7.62 Nato. Most of it is approx 20 grs heavier than commercial 308 cases. A simple rule of thumb is reduce your powder charge 1 gr for every 10 grs heavier your military case is compared to the commercial cases you have used. Like hivelocity has already pointed out reduce that powder charge 10% and work up to start.