The game seems to always use the projectile weights (so what's actually flying). Therefore numbers are overall rather small compared to what real logistics had to transport (propellants/casings/storage boxes). For those interested here's a document regarding the weight of Flak 88mm Shells (see point 34 to see how crazy it can get).
Important note: I am not 100% sure if I've always picked the "correct" Ammonition type, I tried to correlate penetration charts with what's in game and chose therefore that type of ammo. The Brown marked area therefore show such special choosings, where a Assault Gun uses the HE-Shell weight instead of the weight of a Armor Piercing Shell (projectile).
I have created this sheet, it is still WIP and so far I only entered some randomly picked Tanks/SPGs/Artillery to see how things look like. Feel free to "export"/copy it and expand upon it as you like. If you find errors, let me know and I will try to fix them. Sources for the numbers are wikipedia, WT wiki and sites like this blog or this page.
That's the current state.
The red colour (positive numbers) means that this Element is using up too much freight when currently shooting in game.
The green colour (negative numbers) on the other side means that there's too little freight being consumed.
Both are listed on a per shot or per burst (1xRoF) basis.
The last Collumn gives the percentage comparison between IRL projectile and ingame projectile weight.
ALERT: The Sheet uses German formatting, so decimal "," NOT "." !
I am sry for the inconvenience, Mr. and Mrs. Fahrenheit.