Okay, here's my method, but you probably won't like it and many here will scoff at it because it's so seemingly inexact.
As an experiment, I tried mixing various powders, including protein and ala, with var and found that I could never, never get a thorough mix. I tried cutting it in with a razor blade and shaking it in my shaker bottle, nothing worked.
Here's what I settled for. I did one load using 00 caps and egg protein powder, then tamped it down. Did it again, tamped it down. After a second tamping, I found there was about 3mm between the powder and the top of the cap. Then I loaded in the var, tamped it down, packed on the lids. I did this until I had used up 1g of var, divided it by the number of caps made, and used this to estimate the AVERAGE, only the average, of var in each cap. Came out to be about 9.6mg. BTW, I'm using a Capsule Machine, which I like much better than cap-m-quik.