Snap cap
A snap cap is a device which appears similar to a standard firearm cartridge but contains no primer, propellant, or projectile.
Description
It is used to ensure that dry firing firearms of certain designs does not cause damage. Some snap caps can contain a spring-dampered false primer or one made of plastic or none at all, the springs and plastic filled ones help absorb the force from the firing pin, allowing the user to safely test the function of the firearm without damaging the components of the firearm.
A small number of rimfire and centerfire firearms of older design should not be test-fired with the chamber empty, as this can lead to weakening and possible breakage of the firing pin and increased wear to other components in those firearms. In the instance of a rimfire weapon of primitive design, "dry firing" can also cause deformation of the chamber edge. For this reason some shooters use a snap cap in an attempt to cushion the weapon's firing pin as it moves forward.
Snap caps and action-proving dummy cartridges also have usage as a training tool to replace live rounds for loading and unloading drills, as well as training for mis-fires or "malfunctions", as they function identically to a live "dud" round that has not ignited.