I think you guys are saying the same thing, George and Smoke. If I want a 30 grain charge, I weigh 30 grains on my scale and then make a measure which only holds that much. Then I load by the volume held in that measure from then on.
If I had no scale I would start with a pre-sized flask spout or a measure with incremental marks and load by the volume they say is 30 grains. That volume may or may not be actually 30 grains in weight depending on what granulation of powder I'm using but since black powder and it's substitutes are interchangable by volume, it doesn't matter what the weight really is.
In the old days, a man would load with enough powder to cover the ball held in his cupped hand. Then he'd make a measure to hold that much powder to speed up the loading process. I believe that's where we got the whole "dram" thing. Volume was broken down into increments so there was a standard that could be expressed. There was no need to weigh how much a dram was because you had measured it by volume. We don't use drams today in our discussions, we use weight, necessitated by the very different properties of different modern smokeless powders. I can't tell a friend who is loading a 30-06 to put two drams of powder in his cartridge unless I also know what kind of powder he's using and have weighed that volume of it to know two drams is a safe charge. I can tell him to load his muzzle-loader with two drams of powder because that volume has the same properties within the black powder/black powder substitute community.