imported post
I think I may have misunderstood your original post. You're correct about the case I cited. <Matter of Two Seized Firearms, 602 A.2d 728 (N.J. 1992)>. (It's on Westlaw and the hardcopy Atlantic Reporter Second, of course.) A Florida gun owner with two loaded revolvers, one under the seat and the other in the glove compartment of his van was pulled over in New Jersey for speeding and arrested when his firearms were discovered. Although his transportation of firearms in this manner was legal in Florida at the time (1988), it was not legal in New Jersey. The New Jersey Supreme Court held that because he did not comply with 18 USC 926A, it offered no protection for him. Even though he wasn't actually convicted, the NJ Supreme Court held that the state could keep the revolvers it confiscated.
However, although FOPA is supposed to provide firearm owners protection when they transport firearms across state lines, courts don't always see it that way. If you are transporting a firearm that is legal to possess in your state and is also legal to possess in the state to which you are traveling, and you travel through a state where that type of firearm is not legal to possess, you can still be prosecuted under state law, and federal courts don't consider 18 USC 926A to preempt state possession laws.
For example, a Florida attorney who legally possessed a firearm in Florida brought it with him while traveling to visit relatives in New Jersey. He flew out from La Guardia airport in New York, where possession of a handgun without a NY license is illegal. When he declared the handgun at the baggage counter as required by federal law, he was arrested by NY police and charged with possession of a weapon in NY without a license. In Torraco v. Port Authority of New York & New Jersey, 539 F.Supp.2d 632 (E.D.N.Y. 2008), a federal court held that his possession of the firearm was sufficient cause for arrest, regardless of federal preemption. Fortunately for Mr. Torraco, the DA dropped the charges.
I wouldn't drive through California with an AR-15 anytime soon, even if you're only traveling from Oregon to Arizona. It's going to be arrest and confiscation of your weapon, and whether you can persuade a court to enforce FOPA appears to be iffy...
with the handle NavyLT... gotta be current or former Navy JAG, right?