Gas chamber. 15. Gas regulator cup. 9. Magazine top plate. 16. Gas regulator cup. 9. Magazine top plate. 16. Gas regulator cup. 9. Magazine top plate. 16. Gas regulator key. Barrel. 12. Radiator. 13. Barrel Io. Radiator casing. II. 18. Piston. 19. Rack. 20. Main- 17. Gas cylinder, spring. 21. Gear. 22. Charging handle. 23. Trigger. 24. Feed operating arm. 8, Magazine latch. mouthpiece. I4. Gas chamber. 15. Gas regulator key.