P03 thanks for clarifying that, I was on my phone and didn't re-read what I typed. I did intend to say that you would satisfy constructive possession if you purchased a short upper if you also already owned a rifle lower but no pistol lower. If you own both types or no types you would not satisfy constructive possession. I did not mean that you couldn't buy it, as there are no restrictions on upper purchases, but that's what is dangerous about it, that you can unknowingly satisfy that criteria, which is not good from a legal standpoint. My phrasing was also incorrect for the AFG, I meant that it was legal to put on, and this was explicitly stated in the ATF finding.
hotbrass-I only relay what my FFL told me, but from my understanding of what he said that building a pistol from a receiver for the purpose of using the Sig brace is sketchy because it is not legally registered as a pistol, as you stated. He followed the advice that P03 gave, and advocates selling complete pistols for those who want to use the Sig brace just to cover all bases.
I disagree though that you can turn a pistol into a rifle. I assume by this you mean building a stripped lower into a pistol configuration, and then at some later point putting a 16"+ URG and a buttstock on it. While no one would know that it used to be a pistol if it were only registered as a receiver, I can't imagine a pistol with a stock found attached to it resulting in anything good legally.
I do appreciate you guys adding on, I don't get to spend too much time researching this stuff and I'd rather be corrected in public than to be found ignorant and in violation of the law.
