The Desert Tech MDRx 20" 5.56 NATO/.223 Rem Forward Ejection Conversion Kit utilizes the newly designed gas block for enhanced reliability and the new Ratchet compensator. The conversion kit includes the bolt, barrel assembly (including barrel extension), forward chute panel, and magazine insert (if applicable). Desert Tech MDRx Forward Ejection (FE) Conversion Kits are only compatible with MDRx FE rifles and chassis.