Nothing can stop someone who wishes to own a firearm, or any other at least somewhat easily smuggled item, from acquiring said item.
I was thinking of a database containing information about all violent criminals (I assume something along those lines exists already), which the ID of the potential firearm purchaser could be quickly compared with to ensure a violent criminal was not trying to legally purchase a firearm.
How could that database be used against those who legally own firearms?
All a database of that sort would do is force criminals to purchase weapons from illegal sources.
All it would do is make it more difficult for a criminal to acquire a weapon.