When we talk about the receiver, there are two parts in particular. One is the lower, and the other one is the upper receiver. The lower is nothing but the lower frame section, and you do not have to mess it up with the lower parts kit. Thatís something different, and you should know that. I came to know about this through AR-15 Gun Builder. They seem to be a proper resource, and you could ask them for any queries. It would help if you had great clarity before you set out to make your gun. Interaction with AR-15 gun builders shall help you, though!