"Let's be honest. If someone wants a gun, it's obvious the person will not have difficulty buying a gun, either legally or through the extensive United States black market."
Stuff can be done, but ultimately enforcement is an issue, the part of your calculus that is missing. If you can't prevent criminals from obtaining guns now, what good will additional laws do?
Link: https://www.pbs.org/wgbh/pages/frontline/shows/guns/procon/guns.html