Why would Cobbhead have to pay any tax at all if he is giving this shotgun to his son as a gift?
Unless his son needs the gun yesterday, maybe the best solution would be to wait until his son visits him in Colorado, or he visits his son in Kalifornia, and just give it to him personally. No taxes. No FFL Transfer fees. No possible shipping damage. No headaches.
Of course, Obama and all of the Democrat presidential candidates are proposing Universal Background Checks which would mean that all transfers including gifts from a father to son would have to go through an FFL. Of course, this amounts to Universal Registration, and that is the goal. Have you all called your Congressmen and Senators to remind them that you do not want this back-door registration scheme?
