you can use your chargemaster just fine, just have to do it in bits. What I did is used the cap from a Great Stuff spray can (it's like a spray paint cap, but with nothing on the inside, it's just a bowl essentially). You just tare it like a regular pan, fill it with 1000 grains of powder, and do that 7 times.
kind of a hassle for doing more than a pound or three, but it works and it's much more accurate than trusting a cheap kitchen scale (not sure the accuracy on those, but I personally don't like the idea of being out on powder, especially if i'm selling it. would suck to send it to someone and have them tell me i'm 50 or 100 grains short... sure they likely wouldn't truly care all that much, but it doesn't reflect good on me if i'm not sending what i say i will, or more.