It's a mis-marked M-16. An AR-15 is the civilian version of an M-16 and is ONLY sold as a semi-automatic rifle. In order to prevent a civilian semi-automatic AR-15 from being readily converted for use with the select fire components a number of features were changed. Parts changed include the lower receiver, bolt carrier, hammer, trigger, disconnector, and safety/mode selector. The semi-automatic bolt carrier has a longer lightening slot to prevent the bolt's engagement with an automatic sear.