What component in ammunition ignites the gunpowder upon being struck by the firing pin?

The component in ammunition that ignites the gunpowder when struck by the firing pin is the primer. The primer is a small metallic cup containing a sensitive explosive compound that reacts when impacted. When the firing pin strikes the primer, it stimulates the chemical reaction within the primer, which generates a small flash of heat that ignites the gunpowder contained within the cartridge.

The bullet is the projectile that is expelled from the firearm once the gunpowder ignites, but it does not play a role in the ignition process itself. The cartridge is the complete unit that includes the bullet, gunpowder, and primer, but it is the primer specifically that initiates the ignition of the gunpowder. Gunpowder is the propellant that creates the gas needed to propel the bullet but is not involved in the ignition process by itself.