Can't quite get my head around this.

When you measure the weight of a case filled with water and subtract the weight of the empty case to get a water weight in grains then you say that i.e. 100g of water is the case capacity. Then you put 90 grains of powder in the case and say that it is 90% full or at 90% of capacity, isn't that an inaccurate comparison? If you have a box that holds 100lbs of apples and you then fill it with 90lbs of oranges that doesn't mean that the box is necessarily 90% full. If the density of water is different than the density of the powder you use, then there would be a volumetric conversion between the two substances for the same weight. Is the H2O capacity just used for a reference to measure case volume uniformity or to draw comparisons between two different cartridges?

Thanks guys and sorry for the ignorance ;D