From a local manufacturer of lowers: To make a pistol from an AR receiver the receiver must be virgin, having never had a buttstock on it. Once it has had a buttstock on it, it can't be made into a pistol. If you make a pistol from the virgin receiver that CAN be made into a rifle with a sixteen inch or longer barrel. Also don't sweat the pistol marking on a receiver either it is purely cosmetic and means nothing. KevinT