“This one will be disobeyed.”
One of the easiest ways would be for people to “sell” their rifles (to their best friend, brother, etc.), and who in turn “sells” theirs to you. Yes, they can be customized and each one is just a bit different, but the essentially mechanism is exactly the same, so a trade like this is very doable. This way, people will not own the firearm for which they filled out a 4473. There will be MASSIVE non-compliance, so much that it will make the non-compliance during Prohibition look like a joke.