As a non American I can't see a simple solution to the problem, guns are already abundant so banning them won't magically make them disappear, attempting to sieze them would probably cause a dark stain (ala Boston massacre) in the countries history and you've got to deal with the fact that the USA only exists because they had the fire power to make it so which is ingrained in a lot of people.
I wish there was a magical solution but I fear its a choice between a slow, turbulent transition or a quick, brutal, bloody change.