Stock – The stock (or handle) of the gun is usually composed of two pieces (the butt and the fore-end).
Action – The action is really the guts of the gun. It includes all the moving parts that load, fire, and eject the firearms shells or cartridges.
Barrel – A gun’s barrel is the long metal tube, bored out to provide an exit path for the discharging projectile. Once the projectile is fired, it’s forced down the barrel and out of the muzzle by expanding gas forces. In a rifle or a handgun, the bullet travels through the barrel; in shotguns the shot or the slug is shot through the barrel.