Answer:
No this is not legal due to the Second Amendment of the Constitution. This states that "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."
The second amendment was tested recently with the Supreme Court case DC v. Heller, where the Court ruled that a ban on handguns in Washington, D.C. was unconstitutional. So the government cannot ban all sales of firearms and destroy guns at will (this would probably be logistically impossible as well), due to the right to carry a firearm for self defense.