If you're buying a complete rifle, the gun will transfer to you on a form 4 (tax paid transfer) just like a suppressor or a machine gun. If your local dealer doesn't have the SBR and you buy it from a dealer out of state, the rifle has to transfer to a in state dealer on a form 3, then it can transfer to you on a form 4. A form 3 can take anywhere between 3 weeks to 3 months, and a form 4 is running around 6 months right now.
The form 1 is only for manufacturing a weapon (for instance, registering a lower you already own). If you're buying a complete rifle, you FFL/SOT should be able to walk you through the process, but it is very simple. On my last form 4 (for a suppressor) my SOT filled out almost everything for me, printed out the forms in duplicate, and even gave me an addressed envelope to mail them in. All I had to do was put a copy of my trust and a check in the envelope and drop it in the mail.
I assume this is your first NFA purchase. There are two general ways to do the transfer, a personal transfer, and a trust/corp. I personally used a trust so that I could add others onto it so that my family members could possess my NFA weapons while I wasn't present and it also allowed me to avoid the law enforcement sign off (which can add time to the overall transfer by having to send it off to you and get it back before sending it to the ATF).
