noun
cartridge case; shell casing
Refers to the container that holds the bullet, propellant, and primer in a firearm cartridge.
射撃場には薬莢がたくさん落ちていた。
There were many cartridge cases lying on the shooting range.
Compound of 薬 (yaku, 'gunpowder') and 莢 (kyō, 'pod, shell'). The reading やっきょう results from a sound change (促音便) of やくきょう.