On guns so equipped, the hammer is the part that rotates to provide the percussive impact on the primer. The firing pin may be struck by the hammer, or the firing pin may be a part of the hammer. Not all guns have hammers. Many guns are equipped with strikers: notably Glock pistols and the vast majority of bolt action rifles. Hammers may be exposed or shrouded, spurred or bobbed.
The part of a gun lock, which driven by a spring and released by a pull of the trigger, falls and (usually via an intervening firing pin) strikes the detonating primer of the load and discharges the gun. Hammers may be external or internal.