I hope I'm not overstating the obvious, but just so someone doesn't mis-understand, I'll say it: :
Black Powder DOES weigh the same as it's volume in powder measures; it is the standard, and what powder measures were designed to measure.
Black Powder SUBSTITUTES do NOT weigh the same- they are heavier for the same volume.
As CAYUGAD said, a 100 grain VOLUME of 777 onlyWEIGHED 68 grains. It is not wise to WEIGH out 100 grains of 777 or other substitute and think it's a 100 grain charge. It is actually MUCH more!
On your can/bottle of BP Substitute, it will clearly say that it should be used BY VOLUME as a BP substitute. That infers (but doesn't say) that it should not be substituted by weight.
OK - I'm done - just didn't want anyone to get a big SURPRISE!

IM jaybe

everywhere i read said that you CANT weight a charge of blackpowder because powder is MEASURED by VOLUME not weight. thats why i was SURPRISED that geox 2f was so close to weighted charge vrs volume charge.so, i guess reading i was doing was WRONG or they were talking about the substitiute powders as you have said.they always said BLACKPOWDER not others. take care.

YESS,

It just ain't necessary to weigh BP charges, if one isas consistent as you seem to be in throwing them with a volume measure. There'd be no benefit at all, because even a full grain difference in the charge weight of black powder will only cause a variation in velocity of around 30 FPS or LESS!

Since a load can have shot-to-shot variation of up to 150 FPS and still be accurate, there's just no reason to weigh the stuff.

i agree.that 35 year old brass thompson 50-120 measure was very accurate,within .05 to .06 of a GRAIN .