Snap cap ammo is an accessory device for firearms shaped to replicate a live round/cartridge/shotshell but without the ammunition components, which are the gunpowder, primer, propellant, and projectile/bullet. They are used in guns to absorb moisture, to keep bores lubricated, and to avoid damage to the firing pin. There are some snap caps whose false primer is spring-dampened but those are more expensive. Snaps caps are completely passive and produce no sound. Their only purpose is to prevent firing pin/striker damage and aid in tactical reloading practice and dry firing.