Rifle cartridges and shotgun shells have similar designs, share the same basic parts, and depend on the same physical and chemical reactions to work, but are used for different purposes.
The basic components of ammunition are the
case, primer, powder, and projectile(s). Shotshells have an additional component called wad.
case The container that holds all the other ammunition components together. It’s usually made of brass, steel, copper, paper, or plastic.
primer An explosive chemical compound that ignites the gunpowder when struck by a firing pin. Primer may be placed either in the rim of the case (rimfire) or in the center of the base of the case (centerfire).
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.
projectile The object(s) expelled from the barrel. A bullet is a projectile, usually containing lead, fired through a rifle or handgun 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.