I picked up a stripped AR-15 lower receiver at a gun show a while back. My original plan was to turn it into a short barreled rifle. Of course, this requires registering the rifle (or even the parts to build the rifle) with the Bureau of Alcohol, Tobacco, Firearms, and Explosives (BATFE or ATF). Since it can take a while to complete the registration process, I decided to use the lower receiver to build an AR-15 pistol, instead.

I can then go ahead and register my intent to build a short-barreled rifle with the ATF. Once I complete that process, I can simply buy a stock and attach it to the gun. I got a great deal on an AR-15 pistol upper receiver kit so now I can assemble the pistol.