I picked up a new upper for my AR today 16" flat top, with a Holland Quick Discharge Brake
http://crankgoboom.com/guns/ar/AR_16upper.jpg
http://crankgoboom.com/guns/ar/AR_16upper1.jpg
http://crankgoboom.com/guns/ar/AR_brake.jpg
http://crankgoboom.com/guns/ar/AR_uppers.jpg