This is from the FAQ's page of Blackhorn 209.

Question: Can I weigh my charges?

Answer: Yes. If you prefer to weigh charges, you can convert the volume load recommendations into weighed grains by multiplying the volume load by 0.7. Example: 100 units by volume x 0.7 = 70 grains by weight. 110 volume charge x 0.7 = 77 grains by weight.

I posted facts when I answered the question. Grouse posted what he thought then went on to scrutinize loads in a TC Pro Hunter.