I'm new to this Muzzle Loading also.
I went to Cabalas and got a bunch of those little plastic tubes with scales for "grains of BP". On my TC Omega I use right at 100 grs. but by volume.
I took one of those plastic tubes and filled it with BP to the 100 gr mark. Then I filled one with Pyrdex, the with Triple 7, all to the 100 grn mark.
Then I weighed them. It took different weights to make up the same volume.
BUT when I ran them through the crony, they all had about the same velocity and impacted about the same place on target.
Then when I tried loading by weight instead of volume, I got all kinds of variations.
(That wont work with smokeless powder).
Anyway I decided to stick with volume. I just pre-measure a bunch of load in those plastic tubes (mentioned above) and I'm all set.
But like I said, I'm new to ML, so take what I say with a grain of salt. Go see what your own experiments come up with.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071