Let's say I buy a lower with the intent on making it an SBR in the future (6 months - year). Do I need to register it form 4 when I purchase and do all the crap then, or can I do a form 1 when I decide to put the short barrel on it? I'm assuming form 1 but wanted to double check with those that have NFA experience. Eventually I want to have the SBR with full auto and silencer, will adding these to it after it's registered as an SBR make any difference or do I just form 4 the parts as I buy them and add it onto the SBR?