i would agree that weighing charges is often more important to the shooter than to the gun.
that said im not completly sold on the volume theory. powders do vary in size and intensity considerably.
a load of 2.5 gr. of bullseye would be difficult to detect in a 38 special case. yet 3 gr. would make a
major difference and cause it to be at least unpleasant to shoot.
i use a 60 year old belding & mull powder measure which i feel is one of the best designs ever created.
there is of coarse the main container for the powder. then there is a small resevoir which holds a much
smaller ammount of powder. that eliminates the full weight of the main container from affecting the charge.
regardless as to the ammount in the main container the resevoir controls the charge. then there is an adjustable
drop tube into which the powder is dispenced before dumping it into a scale or directly into the case via a funnel.
but the initial adjustment of the drop tube is done by weight. how else could it be done?
i frankly dont always weigh my charges. i make sure the drop tube is adjusted properly and will periodicly check it with the scale. i systematicly charge all cases in the block then check by row to assure all are filled to the same level. sometimes the larger grained
powders will jam up in the drop tube. but thats rare and you can usually sence or see that as it happens due the the ammount
remaining in the resevoir. i dont think a half gr of powder varieation means anything as for group size especially with the slower burning ones. does the ladder test not confirm that?