It would be helpful to find out why he won't sign the Forms. My understanding is that some won't sign because they are worried about the their personal or the cities liability if someone uses a NFA item to commit a crime that he has signed off. He could also be worried about if it could be used against them in an election. There are probably other reasons too. You could tailor your arguing points if you knew the reason he won't sign. Your point about supporting some gun rights but not supporting NFA stuff would definitely be worth arguing along with any other points.