These are made for the 45acp conversion on the FN FAL rifle using either the Thompson M1 or the Grease Gun m3 magazines. They use the factory recoil spring. They can be a bit picky. They are missing the firing pins but do come with extractors. Specify if you want metric or inch set up. Limited to what you see. These were made by cross pinning the carrier to the actual bolt and machining the locking system off. Used for the 45acp conversion in blowback only.