spent casing

Spent casings are often erroneously referred to as bullets. In actuality, they are what is left in the chamber of a gun whenever after an ammunition_cartridge is fired. As such, they must be ejected to make room for the next round.

This is why whenever someone is firing an automatic weapon, you will see brass flying over their shoulder. Those are the casings, not bullets.

Automatic weapons are referred to as such because they eject the casings without any manual input by the shooter, aside from firing the weapon. Other weapons have to be cycled between each shot.

So whenever someone's firing a fully-automatic weapon, expect to see a lot of casings.