Despite the moderator status and 8000posts your yelling is just WRONG (this time)
1) no such thing as volume grains -, its a measure of weight.
2) the volume of measures is calibrated so that the volume marks represent grains weight of common commercial powders
3) if the measure is from any half decent manufacturer it will be close enough to its marked weight that it will not be dangerous
4) there is some variation in the density of commercial blackpowders, and also variations in the energy of them (Swiss vs Wano fr instance) but its not enough to generate a dangerous situation if equal volumes or equal weight loads are used
this pertains to real blackpowder - if you are talking about fake substitutes (eg pyrodex et al) that is a different matter - the directions for reduced weight loads of that are on the can (or were last time I saw one)