Like you said above, weight can be different from volume. That ain't so. There ain't no scale that measures volume. It measures weight, then the weight is converted to a volume.
Smoke got me started on this, again. A teaspoon as used in cooking is a given volume. A tablespoon, another. Would you charge your Rem with a teaspoon of powder, without knowing how much it weighed, in BP terms?
You gots to weigh your thrown charge to see what it is. A given volume of BP weighs so much, and if your charge is over or under that, as measured, then you are at a disadvantage. An 1860 shooter weighs 30 gr and makes a measure drop that, and you shoot your 40 gr, and he shoots thru a 6 inch log, and you can't, what is the problem? Damn, them 60s shoot hard, why don't they fall apart? I gots a topstrap..
A balance scale is not that expensive, at least I don't think it is. Mine's 40 years old, a Lyman Ohaus. Still works perfectly. That's one thing about strictly mechanical balances. They always work the same way.
Gone to bed now, had more than enough of this for one night.