Do not confuse measures of weight with volume. This is what makes mistakes and gets people hurt. Glad you asked your question.

Your shooting two triple Seven pellets right now. I would try loading 70 grains of BlackHorn 209 BY VOLUME. Meaning take a powder measure and set it at 70 and pour your load that way. Using a powder measure work up your most accurate load. Be that 85 grains or 100 grains... what ever. They say not to use more then 100 grains by volume but I know some shooters do. That does not mean I recommend you do the same. Let your rifle tell you what load it likes.

THEN IF YOU WANT

Take that lets say 100 grain BY VOLUME load your rifle loves, and weigh it on a scale in grains. It should weigh right around 70 grains. You can then use your scale and say ... weigh out several 70 grain loads.

VOLUME in GRAINS BH209 X 0.667 = WEIGHT in GRAINS BH209 Here I believe 6x6 is talking about a 100 grains charge BY VOLUME that he weighed out. So 100 grains of BlackHorn 209 BY VOLUME weighed 66.7 grains on a scale.

http://www.blackhorn209.com go to that site and look at their load data. It will explain it better to you I think.