Not a part of a firearm -
Parts of firearm weapon are:-


Barrel: Which has two ends: breech end and muzzle (breech end may have a chamber and an extractor).
Action: Consists of

(a) breechblock (bolt),
(b) firing pin or striker pin or hammer,
(c) trigger.

Grip (buttstock and magazine.
Bolt
Piston
Extractor
Muzzle