People keep talking about taking guns.
I agree that won't work.
But don't a lot of these lunatics go buy the gun, pop the tag, then crash out?
So I'd say start by not manufacturing thousands of new guns. Outlaw ammo. Sure people can make their own ammo, but you not gonna make 1000 high tech armor piecing hollow points. You gonna make a handful of shytty bullets. If we're lucky the person kills themselves when their first shytty bullet malfunctions.
Then, if machine guns are not allowed in public, which they really shouldn't be, the cops can cop out on anyone they catch with one outdoors.
Eventually the existing guns have to bleed out of being usable. That part will take a very long time, but we can start to REDUCE the number of mass shootings instead of what's happening now.