A snap cap is a device which is shaped like a standard firearm cartridge but contains no primer propellant or projectile. It serves the same function as a dummy round but different in that a dummy is usually made from a real cartridge with its propellant and primer removed (still has the projectile and the casing) while a snap cap is designed to be a fake cartridge from the very beginning.A snap cap is used to ensure that dry-firing firearms of certain designs does not cause stress and impact damage to the firing pin and/or the barrel breech. Some snap caps contain a false primer that is either spring-buffered made of rubber or soft polymer or none at all. The springs or plastic will absorb the impact force from the firing pin during dry-firing allowing the user to practice trigger pull or safely test the function of the firearm action without damaging its components.