In the recipe for reloadedd 9x18mm +P+ (I think it’s part of a mod, maybe Artyom’s Gun Emporium or Icecoon’s Weapons Pack) it takes 10 9x18 casings and
10 primers to make 25 bullets. I also think it takes not enough gunpowder and metal, but I’m not sure.
When firing a 50.cal or the m240 from a tank, casing fall outside. If you think about how a tank is built and how machine guns are positioned, that’s pretty much impossible. They should fall inside the tank, on the floor.
EDIT: also it appears that empty tanks weight as much as the ones filled with liquids, when mounted on a vehicle.