"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Since the right to keep and bear arms is due to the necessity of a "well regulated Militia," all gun owners must 1) register all firearms, and 2) join the National Guard, including spending one weekend/month and two weeks/year in training. After all, per Article 10 of the United States Code, National Guard members are part of the Militia.
Let's give all of the frustrated, would-be soldiers - so willing to protect their country - the opportunity. Time to put up or shut up.