The MDRx Black Chassis features upgrades to the chassis' construction and trigger assembly. The MDRx chassis has been upgraded with a polymer resin that is more resistant to high impacts and the gas block drainage has been improved so that the rifle functions more reliability in wet or muddy conditions. The trigger in the MDRx Chassis has been improved so that it has a lighter pull weight and less creep resulting in better overall accuracy. Desert Tech MDRx Side Ejection (SE) Chassis are only compatible with MDRx Side Ejection Conversion Kits.