I have proposed a solution here a few times. Instead of registering guns and limiting magazine sizes and whatnot, we should register gun buyers.
If you apply to be a gun buyer, and pass a mental health and criminal background check, your name goes on a list. Sort of like those people who can now get pre-screened before flying.
If you wish to purchase a firearm, the retailer simply looks to see if your name is on the approved gun buyer list. If it is, you can buy as many guns and any size magazines you wish, and no record is kept of what you bought.
If you are a certified nutjob, your name does not get on the list and you cannot buy a gun.
If you are on the list, and then get convicted of whatever crime the people of your state decide warrants your removal from the list, then you are taken off the list.
If you are on the registered gun buyer list, it does not necessarily mean you have bought a gun. Nor does it indicate how many guns you own. Nor does it indicate how much ammo or magazines you own. It just indicates you are an upstanding citizen whose Second Amendment rights shall not be infringed or taken away without due process.