AR15/M16 Bolt Carrier Rebuild Parts Kit After the round count starts to pile up, your rifle may benefit from a Carrier rebuild. Here are all the high quality parts required to bring your Bolt Carrier back to like-new function: M16 Firing Pin, Firing Pin Retaining Pin, Cam Pin, Gas Key and 2 Gas Key Screws, a set of 3 Gas Rings, an Ejector Cartridge, Ejector Spring, Ejector Spring Pin, Extractor, Extractor Pin, Extractor Spring, Extractor Spring Insert, and Extractor O-Ring.