The WE Open Bolt M4 Kit will allow you to convert your old AWSS M4 (Brass Bolt System) into the new realistic Open Bolt system. The kit includes a completely assembled Inner Barrel with Hopup Assembly (inner barrel, hopup bucking, hopup shell), a complete Bolt Assembly (bolt housing, nozzle assembly), Complete Trigger Group, magazine lip/seal conversion set (follower, mag seal, mag lip), and other small parts necessary for the conversion.