Empty shell casings are allowed in carry-on bag as long as the projectile is no longer intact. They are allowed only if the primer has been removed or has been discharged. If the projectile is attached & the powder has been drilled out, it is considered a replica and not allowed in carry-on.
Shell Casings
Carry On Bags:
Yes (Special Instructions)
Checked Bags:
Yes
The final decision rests with the TSA officer on whether an item is allowed through the checkpoint.