The Desert Tech MDRx 16" 5.56 NATO/.223 Rem Side 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), ejection panel, and magazine insert (if applicable). Desert Tech MDRx Side Ejection (SE) Conversion Kits are only compatible with MDRx SE rifles and chassis.