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So my Sunday am hasn't been that interesting if I'm honest, so there was nothing else to do whilst watching Lovejoy re runs than to measure some case volumes.

Interestingly (and I appreciate that this may be a personal thing!!) the results weren't as expected. There's not too much info on t'interweb on methodology so I made a "best guess".

Weighed 5 fire formed and still primed cases (each) of GGG 7.62 Bisley surplus and Seller & Bellot .308.

S&B averaged 181.06 grains - variance of 2.62%
GGG averaged 176.86 grains - variance of 0.15%

Filled carefully with water to the brim with a syringe, reweighed and volume calculated:

S&B averaged volume of 55.4 grains (variance of 2.62%)
GGG averaged volume of 55.7 grains (variance of 1.19%)

I'd always been led to believe that mil surp case volume was less than .308. Also the GGG would seem to be more consistent in weight and therefore volume.

What else does it tell me? Probably that I need to get out more.

It tells you what it told you, ooman. Now, as to interpreting the findings, that's a whole new kettle of piscatorial puzzlement. Dromia may be along in a minute to elucidate...

Were they trimmed to the same oal?

Yes - they were before they were fired (Lee case cutter). I've found that the S&b actually expand more than the GGG.

To be honest, I'm not exactly really what it means in practise, other than I've been cautious reloading for the GGG as i was told the capacity is less.

Maybe I'll try it once I've resized and trimmed.

QL has 7.62 NATO at 52 gns H2O maximum case capacity and 308 Win 56 gns H2O maximum case capacity both with a case length of 2.014.

What it tells you is don't believe everything you read and now you know what your case capacities are.

GGG seems more consistent brass that S&B.

Cautious is good however the target along with safe, methodical, diligent, load development will tell you what shoots best with your components in your rifle.