Start ALL Builds as Pistol! Why not? If I start my AR build as a pistol, I can then use the same lower for Pistol AND Rifle uppers. I can switch back and forth without any legal issue as long as I take off the stock. Does everyone do this to preclude any issues when switching uppers, if not why? What are the downsides to this? I just put my lower together, but have not attached a butt stock or barrel (don't barrel yet) and this question keeps popping up in my mind. Should I just snap a pistol upper on first? Wanna kill these ads? We can help!