That seems like a gray area. Are there any precautions I should take? For example, what if I'm transporting to the range a 556 non-sbr and a 556 sbr with an additional upper and said upper could be pinned on either lower? Do they just see that I have a registered sbr and I'm good to go, or could they consider the possibility that I could easily possess two sbrs and only one of them is registered?As many uppers as you want and in any size/caliber you want. And thank you.