sentences:  Upon firing, the bolt carrier and striker assembly recoil to the rear and the geometry of the fixed camming surfaces drives the rollers inward unlocking the bolt breech and increasing the speed at which the striker sleeve withdraws relative to the bolt.As the slower bolt continues rearward it impacts the returning striker sleeve (this impact decelerates the bolt).The bolt assembly also contains the spring extractor, while a lever case ejector is located at the base of the feed tray.