Burden of proof in most criminal procedures is on the state to make it's case. They would also have to find someone at the ATF that actually cared. The state ain't getting the BB / 4473 without fed involvement, most of the time. Think about the amount of work required to even prove that....Well it would be easy for them to prove if its never on a pre-94 FFL book as a rifle. Then the onus would shift to you to prove that it was a rifle prior to the cutoff. Good luck with that! I've never heard of it happening either - yet.