One downside to the LH Uppers that fit on standard lowers is the ejection port cover is held up by a spring to clear the bolt catch vs on a RH upper it is held down .
Ask me how I know...first trip to the range with my new LH Stag AR first shot went great...second shot pulled the trigger and nothing. Ejection port cover spring had broken turning the gun into a single shot as the cover prevented the fired case from ejecting.
