[NWPilgrim]

OK, I changed the weighing method to weigh empty case, fill with water and weigh the filled case on scale, subtract original empty weight to get weight of water in grains.

Again, this is just an informal comparison of RELATIVE case capacities to investigate any difference between military and commercial brass in .30-06 and .223. I am not attempting to measure the actual fired case volume for use in pressure calculations. While this is not a statistically valid sampling, the samples selected were representative of their headstamps for my purposes. I would consider anything within 0.5 grains as insignificant for relative comparisons.

New results for .30-06
Headstamp, empty case gr., water gr.
Military cases
HXP____194.0___68.8---[outlier]
WCC___193.0___68.0
SL_____197.3___68.0
LC_____198.9___67.9
TW____198.9___67.8

Commercial
Win____192.8___68.3
R-P____200.9___68.0


Considering the empty weights varied from 193 gr - 200.9 gr, it is surprising that water capacity only varied 67.8 - 68.3 gr except for the HXP and the two extreme empty weights had exactly the same water weight.

New results for ..223/5.56
Results in Grains of Water
Military
LC____95.2___31.0---[outlier]
WCC__95.9___30.4
CJ____96.6___30.4
MAI___97.1___30.4
TW___97.1___30.2

Commercial
PMC______95.2___30.8---[outlier]
FC small___94.4___30.6
FC large___96.6___30.4
Win______96.1___30.2
R-P______94.2___30.1
Fiocchi___101.5___29.9
S&B_____107.0___29.2---[outlier]

Overall, this seems to confirm at least informally there is no significant difference BETWEEN MILITARY AND COMMERCIAL case capacity for these two cartridges. There is more variation within either military or commercial than between the two types.

Welcome any additional data points others want to share on their own measurements or findings.