As a dealer, I've been selling stripped lowers. On the 4473 form for type of firearm, I list them as "receiver". I also list them as "receiver" in my A&D book. When calling NICS, I say sale of other. I assume I'm doing this correctly? I had a guy ask if these lowers were "registered". I assumed he meant if he had to complete a 4473, but he was meaning if he had to use the lowers for only a rifle build or if he could use them for a pistol. I told him he could build either, but that I had read that a rifle build would always have to stay a rifle, it couldn't be changed back to a pistol. Then I got to thinking, why though? Say a guy builds a rifle and decides he wants a pistol instead. Why can't the guy disassemble the gun, sell the stock and buffer tube and put a pistol tube on and rebarrel the upper? As long as there is no stock present in the home, there's no way to show intent for an SBR, right? And since the lower was bought stripped and sold as a receiver, there's no record that it was neither a rifle nor a pistol, right?