It's going to be a long-term thing, to be sure. Just a suggestion:-

How about legislating that all firearms must be licensed by a competent body after a rigorous process of application [like here in the UK]; every unlicensed weapon to be handed in within a reasonable period -- say 6 months: after which possession of an unlicensed weapon would become a federal offence punishable by a 10 year sentence?

Something along those lines might just work. Why not give it a whirl?

≈M≈

Now come on -- let's hear all the reasons why such a process couldn't possibly work in the freedom-loving USofA...