The original makers of BH always stated that the powder was designed for volume measure. 120 grains was max.... in regular, store-bought guns that had a max of 150 grains by volume of black powder or appropriate subs. Custom guns or modified factory guns may have different maximum capabilities. I guess like measuring out the charges and then re-weighing them to determine what the average weighed weight is, you could volume measure ten at 120 grain of one particular lot of BH and then weigh to get the average which one would then consider the max weight. People weighing the charges still need to be mindful that the recommended max is 120 volumetric grains, regardless of whatever the average weighed weight is based on lot to lot variables. Change lot numbers of BH? Take time to measure by volume and re-weigh to get an average weight for you load.
Encore....you've mentioned numerous times that at your big shoots you can not load any higher than 120 grains. Is that a vloume measure or is it a weight measure? I'm assuming volume and if so are you averaging the volume charges out to get a weight which would be much more controlled as far as accuracy at distance would concerned?