It measures just like all the other subs. You can use your same volume measurer that you use for 777 as BH. If you were shooting 2 777 pellets (assuming they were 50g pellets) you can measure 100g of BH and you will be close.

If you're going by WEIGHT, that's a seperate topic. I don't weigh charges so others can help you w/that.

In fact, switching between 777 and BH for most loads I have found changes the POI very little.

Hope this helps