I will say that this is very true in .308 but less so in .223. I have done a bunch of case volume measurements in .308 and .223.
All cases sized and trimmed to the same length, primer installed. I did 2 of each year or batch.
IVI 85= 32.7/32.8
LC 01= 32.8/32.8
LC 04= 32.2/32.2
LC 92= 31.8/31.9
WCC 84= 33.5/33.3
WCC 01= 32.8/32.7
FC = 31.7/31.6
The WCC and FC are commercial cases All the rest were Mil. In this case the higher pressures would be in the FC cases and the lowest would be in the WCC cases, both commercial. Just some thoughts.
As with any load you start small and work up.