At least in CA this is not an issue. It is, as of January 1, specifically illegal for a CA resident to import ammunition into CA. That includes internet purchases or buying ammo out of state and bringing it back in with you. ALL new ammo purchases in CA must now be conducted face-to-face in a retail store specifically licensed to sell ammunition. (You can buy it out of state and shoot it there, but if you bring it back across the border you are committing a crime and could be arrested for it.)