 While this option works well, it requires the use of lower iron sights and optics.In 2019 Brownells, Inc. released BRN-180 complete upper assembly, a new take on the AR-180 design built around the AR-18 short-stroke piston system.The BRN-180 is designed to be fitted to mil-spec AR-15 lower receivers and unlike standard AR-15s the BRN-180 can be fired with the stock folded.