Although FOPA supercedes any state or local restriction for transport of firearms, it is an affirmative defense and the burden of proof is on you to prove that you were not in violation of the law. NY and NJ troopers frequently disregard the law and will charge you with possession of an unauthorized firearm or some such nonsense, even if you are on an uninterrupted trip through their state, your firearm is unloaded, in a locked case, and is inaccessible to the driver and all passengers. My wife and I travelled through upper NY state this last year on our way back to Ohio. I had a bolt action .300 Blackout rifle, a Five-seven, two suppressors, a Ruger 10/45, and my Colt M4. I was pulled over by a NY State Trooper while driving the back roads of NY and literally within sight of PA (about 500 yards). He insisted that we get out and that he be permitted to inspect the bed of my truck. Everything was locked in cases inside my truck bed, which also had a locking bed lid. He proceeded to interrogate my wife and demanded to know why we had illegal weapons. She informed him that everything was legal in Ohio and every state that we stopped in. I provided him with a copy of our NFA trust, a letter from BATFE to our congressman that clarified the situation that NFA related items are equally protected under NFA and also provided him with a copy of the Don Young letter re: FOPA. Nevertheless, this involved over an hour and a half delay and unnecessary hassle. Were it not for the fact that I had all my paperwork in order (copy of the trust, copy of cancelled tax stamps, copy of FOPA, copy of Ohio Revised Code, Don Young letter, BATFE letter) and kept my receipts to show that I had an uninterrupted journey, I would have gone to NYS Pound You In the Ass Prison.
Avoid NY, NJ, and all other draconian states at all costs.
I have a copy of the letters available to anyone who sends me a private message.
Uncle Duke