Basic Components of Shotgun Shell

The basic components of shotgun ammunition are the case, primer, powder, projectile(s), and wad.

Glossary

case: The container that holds all the other ammunition components together. It’s usually made of brass, paper, or plastic.
gunpowder: A chemical mixture that burns rapidly and converts to an expanding gas when ignited. Modern smokeless powder will burn slowly when ignited in the open (outside of the case). Black powder is less stable and can be explosive when impacted or ignited in the open.
primer: An explosive chemical compound that ignites the gunpowder when struck by a firing pin. Primer is placed in the center of the base of the case (centerfire).
projectile: The object(s) expelled from the barrel. A slug is a solid projectile, usually of lead, fired through a shotgun barrel. Shot is a group of lead, steel, tungsten alloy, or bismuth pellets fired through a shotgun barrel.
wad: A seal and/or shot container made of paper or plastic separating the powder from the slug or shot in a shotshell. The wad prevents gas from escaping through the shot and holds the shot together as it passes through the barrel.