Load your "rifle" Harrell dump with propellant.  Tap the bottle with your finger until you believe the powder bed is settled (a good few taps).  Set your vernier scale to 156.5 dingle units.  Dump one powder charge, and put it right back in the top of the reservoir.  Dump a second charge and weigh it in grains. Record that weight.  Do it a few times.  Take the average. That average weight should be your effective "gravimetric density" for THAT propellant.  To clarify:  The 156.5 setting on MY "Rifle" Harrell dump corresponds exactly with 100 grains of water (1 gram/cc).  As your powder density decreases from water, this vernier setting should give you the resultant density.   Next, the calculation to dump a precise charge (should be verified with a scale!!):  CHARGE WEIGHT X 1.59/VOLUMETRIC DENSITY = YOUR VERNIER SETTING.

Ashley says this process is like "FM", which I think stands for "Fancy Magic".