This device was created to give you a realistic dry fire experience while ensuring you will not damage your equipment. It installs through the top of the magwell before placing the upper onto your lower. Very easy to use. A lever on the side (towards the shooter) allows you to reset the trigger without breaking your position. The size and profile are the same as the 20 round magazine used in highpower. A great option for your off-season training A handy tool for any coach Works with any AR-15 Mfg: White Oak Armament