Please do not advise posters to break the law. If he did as you suggested he would become a criminal. If for any reason the police investigated his weapons, and it happens to good people (neighbors or co-workers with a grudge could easily call the police on you for anything), they will find his "Assault Rifle." He will have his name published in the paper, he will have his house, face and evil weapons shown on television, he will be arrested and he will go to jail.
Unless you can prove the rifle and accoutraments that make it an "assault weapon" in NY were all present BEFORE the law went into effect your defense is DOA.