The Citizens of each State shall be entitled to all Privileges and Immunities of Citizens in the several States.
If you are immune from prosecution over owning firearms at the Federal level, then you are immune at the States level.
When in doubt see Art VI, para II
This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.
And just in case that isn't unambiguous ENOUGH... they then went on to add in the 10th and 14th which are VERY real amenments that were fully ratified.