Busta, I was taking a guess, but I glad you posted your results. 
The only black powder I weigh is actual Black Powder and it is different than triple 7. In Black Powder for my Shiloh Sharps 45-70, 70 gr. Volume is 73 gr. of actual weight.
Redhawk1,
That is a fact with Black Powder that you understand, since you load by weight and understand the volume to weight ratio. I try to tell some of the guys who shoot Black Powder that I get a lot more shots per pound with 777 since the weight to volume ratio is much more favorable.
By taking your example of 70 GBV (grains by volume) = 73 GBW (grains by weight), that would mean that you only get 95.89 shots per pound of your particular type of black powder. Each brand may be slightly different by weight, but all should be right around the volume measurement, since that is what all volume measures are supposed to be regulated at. I have not actually shot real BP since the late 80's or early 90's.
If we used your brand of BP (Black Powder) for example, 100 GBV would equal 104.285 GBW. That would be 67.123 shots per pound. Now take the 777 FFG example, 100 GBV (77.7 GBW) equals 90.09 shots per pound.
Now to make things much more confusing, but to show the economical side of that "expensive" pound of 777. 85 GBV (66.045 GBW) 777 FFG would be the equivelant to 100 GBV (104.285 GBW) of your Black Powder, since we all know it is aprox 15% "hotter", for lack of a better word. So now you add that into the equasion, 85 GBV (777) would weigh 66.045 grains and would net you 105.988 (100 GBV Black Powder equivelant) shots per pound that you would only get 67.123 100 GBV actual (104.285 GBW) shots per pound of your brand of real Black Powder.
To take it further, 70 GBV (73 GBW) charge of your BP, could be reduced 15% with 777 FFG to 59.5 GBV (46.2315 GBW) for equivelant charge. That is where the real economy of 777 starts to show. The 777 59.5 GBV (46.2315 GBW) load would be approx equal your 70 GBW (73 GBW) load of Black Powder.
70 grain BP equivelant (59.5 GBV, 46.2315 GBW) of 777 FFG = 151.41 shots per pound.
70 grain equivelant (73 GBW) of your Black Powder = 95.89 shots per pound.
55.52 more (70 grain equivelant loads) shots per pound with 777. Try to explain that to most traditional shooters and they will look at you like you are from Mars, or worse.
Now I would imagine there would be a point in the lower charges somewhere that the 15% rule might not be an accurate measurement in a velocity sense, but I don't know where that would be. Someone with a lot of time and a Chrony would have to tell you that.
I just hope my math wasn't "fuzzy"?
