Private sales (between two non-FFL individuals) devoid of any paperwork are still legal in most states.
I live in one: Texas.
This, coincidentally, has a complementary effect, if you live in such a state. The Obamaniacs come around and ask for the AR, you claim you sold it to a private buyer a few weeks before the ban went into effect. Unless you’re really unlucky and are one of the first people they went to (unlikely) you will have gotten enough warning to hide your weapons where the Obamaniacs won’t find them.
Of course, if they’re going door to door, it may then be time to begin to consider USING the rifles once they leave your premises.
Going door-to-door is unlikely. They will hit one place, then another elsewhere in town, then come back later. Resisters will be dealt with violently and possibly WACO'd to provide examples of what happens to those who defy the state and cow all but the most ardent resister into submission.
Searches (they won't take an "I sold it" at face value) will destroy the homes and property of those who do not hand over arms, and anything of value will be looted as well.
Mark my words. This is an illegal and unConstitutional act.