Firing Pin
Also: Striker
The spring-driven pin that strikes the primer to fire the cartridge. In most bolt rifles it is a striker carried inside the bolt.
When the trigger releases the sear, a compressed spring drives the firing pin forward to dent the primer, crushing the priming compound and igniting the charge. In a bolt-action rifle the pin is a striker that lives inside the bolt and is cocked as the bolt is cycled.
The interval between sear release and primer ignition is lock time, and a light, fast pin behind a strong spring shortens it. Short lock time means less chance for your aim to drift between break and ignition, which is one reason crisp striker systems matter to precision. A firing pin that strikes too lightly causes duds or hangfires.