Bullet shell casings immediately disappear into the ground after firing
Ideally they would persist for some time - and have a basic amount of one-way physics to bounce/collide with the ground or buildings or pile up after being ejected
This would add to the immersion of being in a battle or visiting the site of a battle afterwards
Not something to be replicated over the network for performance sake obviously, but just local to the players within a certain distance of the fired weapon