case H2O capacity vs powder capacity?

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

Yes, it is for comarison only. Water fills the whole case. Powder density varies from powder to powder as does the air space around it.

Thanks Ed!

I use quick load and input the water capacity, but never thought about it that way untill your post.

Heres a theory I just had. Unlike powder, whos volume changes based on the type of power. Water does not.
XX weight of water is always gonna equil XX volume, it wont change. Unlike power. So using that theory, you can calculate how much usable volume you have based on water capicity. My guess is that quick load used the waters weight to calculate the case capacity. And since it also has almost every powder in there, it probably knows the volume of X grains of Y powder.
Using only one type and lot of X powder, XX grains of it is probably gonna always take up the same ammount of volume. The real fun in all of this is doing the math, witch I am not that good at. :)

Dividing the weight of the water in the case by 252.777 gives you the cubic capacity of the case in decimals. This gives you volumetric area and thus loading density.

My first computer predates Quick Load because the modern computer hadn't been invented yet. Below a Powley Pocket Computer from 1968 for computing load density, it is in such good shape because your reloading data in the reloading manuals covers 70% of the information this computer gives you. (so why bother) The problem is loading density does not go hand in hand with barrel vibrations and accuracy. Meaning the perfect loading density doesn't always give the best accuracy so you still vary the amount of powder to find the sweet spot.

[img width=600 height=257]http://i122.photobucket.com/albums/o254/bigedp51/powley-3.jpg[/img]

Online Powley computer, click below.
http://kwk.us/powley.html

Been a while since I've seen one of those bigedp51!

I use the water weight only as a reference to compare case volumes.