[The Fed]

There is no national gun registry but each gun store keeps their copy of the 4473 for forever. I can see where the BATF simply amends their (federal) regulations to accomplish new gun control. They can easily amend their regs by simply publishing the new requirements in the Federal Register, waiting the required waiting period then implementing the changes. They can require all firearms transactions to be performed by a FFL - there's already a clause that states federal law is the law of the land. And they can also classify certain firearms and magazines as contraband. Already happened before. I wrote changes to federal purchasing regs that were implemented so I know it can be done.