I'm looking to start purchasing parts to build a pistol AR.....If I were to order a short barrel from online like maybe from Rock River Arms or whomever stocks them, do the barrel's get shipped direct to your home address or do you have to provide FFL info when ordering?....it's just the barrel itself I would like to order as I would order the upper receiver elsewhere or whenever I can start putting pieces together for the build.......And question about a lower receiver. Since the lower is considered the actual serial numbered firearm part, does it need to be engraved with the words Pistol on. I mean obviously the build will not have a stock and just the pistol buffer tube unless I use the Sig arm brace on it for arm support purpose until I get a tax stamp if I go that route, but when purchasing a short barrel, how does the seller / dealer know whether you are building a pistol AR or a SBR ???