Thread: Case capacity question.

Greetings Andygr,
I have made a bit of a study of .308 W case capacity. Cases on hand range from 155 grains for Super X (older Winchester) to 187 for GFL (Fiocchi I think) or 32 grains variance. Brass has a Relative Density of about 8.8 so about 3.6 grains of H2O or 3.3 grains of powder. This is huge. I have loaded some test rounds to check how much difference this amounts to in velocity but have not chronographed them yet. Based on earlier work with Federal cases (about in the middle of the range) I am expecting about 100 fps more velocity with the heavy case. This would be equivalent to adding 2 grains more powder in the lighter case. The extra velocity comes with extra pressure (about 5,000 psi for a rough estimate) and is likely to land higher on the target. With my original .308 in its wood stock would have printed about 50mm higher at 100 metres.
You are on the right track Andygr, with weight batching. This is what I do but still keep head stamps separate. I have measured case capacity in the past using ball powder which is less messy than water then converted it to cc's using the powder density. I think I will just weigh the cases in future.
Regards and all the best Grandpamac.