weight vs capacity
yer right case volume is what your looking for. weight is indictitive of volume but not totally accurate. As to case deviation for my 22-250 I use +/- .3 gr. One thing i have done in the past is take a 100 new cases. separate them by weight and keep the 50% that are nearest to the mean weight. This is of course after I have done a full case prep on all the cases.