Ari Armstrong has a piece on the Colorado use tax which law-abiding citizens are supposed to pay on anything they buy on line from out of state like books from Amazon or ammo from Lucky Gunner. In practice pretty much nobody bothers to pay this as doing it correctly would involve keeping the receipts from everything that arrives on your doorstep, not losing any of them, and figuring out what the tax rate is on all of it.
Failure to do this is a class 5 felony.
So if you ever bought anything on line and failed to kick back 4% to the state come tax time, you are a felon and thus ineligible to buy or own a gun. Think of it as a gun control law of convenience, enforceable when and where the government pleases.
Of course if we made violation of this law a disqualifier for holding public office or employment with the government, state or local, we could fairly quickly empty out all those big government offices and save the state a ton of money on operating costs alone not to mention the boost businesses would get from no longer being harassed by pettifogging bureaucrats.