Take one piece of brass. Load and fire it 3 times. Compare this to your new brass. How much brass will expand depends on how your chamber is cut. You could be lucky and have minimal expansion.
ok, it has been fired twice now and it is still the same measurement, usually the new stuff measures 2.7820-30,,,the twice fired stuff measures 2.7830, i measured about 5 out of the 80 or so twice fired. i will measure them all soon but 5 is a good enough sample for now.