We don’t give primers a lot of attention, but they have the most important job in the cartridge “go bang” process. It’s the primer that converts mechanical energy into a small conflagration that ignites the powder charge in the cartridge.

A primer contains a primary explosive, which basically means that it’s unstable and volatile. Propellants are generally considered secondary explosives. They’re more stable and burn with a slower velocity. You wouldn’t want to load a cartridge with a primary explosive as the firing pin strike would simply blow up your gun, and that gets expensive. So, a cartridge uses a tiny bit of primary explosive in the primer that’s volatile enough to ignite from a firing pin strike. This small bit of primary explosive sets off the much larger, and more stable, secondary explosive.