Spent cartridges are not seen when shooting in first person view, but actually should be visible because of their trajectory.
Simple repro: just shoot a weapon and try to see the cartridges. You'll see none.
1.Open editor, place playable unit (e.g. rifleman)
2.Change weapon to pistol
3.Open debug console, execute "setAccTime 0.02"
4.Shoot 4-5 rounds as fast as you can. Press Esc immediately after and select CAMERA
5.Observe the cartridges hanging in air just near the weapon. They, however, can't be seen in first person.