@goldfinger
as for solutions, we clearly need a way of streamlining criminal databases... the Air Force apparently screwed up here.
furthermore, I wouldn't be entirely against a gun registry, as long as it were not public, and only on a judge's grant could someone look into it (to avoid any and all possible targeting - or claims of targeting - of gun owners) and this might help track guns.
the private seller's issue also allows guns into the hands of people with suspect character, and we should consider some basic information to be recorded about the seller, even if the idea of background checks would be too difficult to implement.
ban any easy mods that make weapons fully automatic (it think this one has been repeated quite a bit)
have psychological check ups required for gun owners and confirmed by private (non-govt) doctor, once every X- number of years (that'd be an interesting number to debate)
gun laws restricting ownership (or securing of weaponry) if minors or mentally ill are living indoor household
monitor the southern border for gun transfers (interestingly enough, more guns come from usa TO Mexico than the other way around, but it's still a problem).
monitor the types of equipment used to make ghost guns more heavily (specifically the heavy duty 3D printers that are programmed for these types of things... although I did see a youtube video of a guy making a AR 15 lower, just form melted aluminum soda cans, with carpenter's tools.)
increase gun buy-back programs, especially in inner cities where gun crime is truly devastating. there have been weekends in Chicago alone where 30+ people die, and get no national coverage. this last weekend 5 have died from what I can tell, but it's less dramatic than single shooter incidents that are separate from drug crimes and gang violence.
states could put out a vote on whether or not to offer gun safety and training classes, I mean we have many other government sponsored classes, this could help lower accidental deaths quite a bit.
as for the mass shootings, I'm not sure what specific policy can help, targeting mental health perhaps? but then the mandala bay shooter isn't covered in that... although one could consider that attack unique.
one thing we could do is start a massive ostracizing campaign on this shit. whenever a shooting occurs, focus almost solely on the victims in the media, and whenever they refer to the shooter have it be something like "loser" or "bitch-ass fuck boy" or "that one kid who only eats mayonnaise on rye with nothing else, I mean what a disgusting little cunt" but on a serious note: don't give these people spotlights. at all. attack the cultural aspect, but legislatively that'd encroach on rights for free press so I don't know...
I think gun buy backs would be pretty high on the list for these things, attack the financial greed of the sick mind. the problem would be people abusing the system trying to profit off of selling guns back to the government, but from an incentive based perspective I really like them