Sensible legislation already exists. Before anyone in the U.S. can purchase any firearm, in any state, they must undergo a full background check. You cannot buy a firearm if you: Have been convicted in any court of a crime punishable by imprisonment for a term exceeding one year;
When it comes to handguns, almost every state has requirements for carrying pistols, which often include requirements for training, supervised range time, and, yes, more background checks. When people start wringing their hands about needing more legislation to keep guns out of the hands of the wrong people, I immediately know that they're just spouting bullshit and don't have a clue what they are talking about. We already have sensible legislation. What we don't fucking have is adequate care for our mentally ill. We also don't have a society that has any resemblance of economic parity, and one that demonizes 50% of its population for being the wrong gender. Gun control is just a shibboleth. The real key to dealing with gun violence is not the guns, but the underlying mechanisms leading to their misuse.
I repeat: This is a national requirement, not state. Most states impose their own, additional conditions; in my case, simply to purchase ammunition for hunting, I had to pass a secondary background check and pass two courses, one involving hunting and one on gun safety. Are under indictment for a crime punishable by imprisonment for a term exceeding one year;
Are a fugitive from justice;
Are an unlawful user of or addicted to any controlled substance;
Have been adjudicated as a mental defective or committed to a mental institution;
Are illegally or unlawfully in the United States;
Have been discharged from the Armed Forces under dishonorable conditions;
Having been a citizen of the United States, has renounced U.S. citizenship;
Are subject to a court order that restrains the person from harassing, stalking, or threatening an intimate partner or child of such intimate partner;
Have been convicted in any court of a misdemeanor crime of domestic violence.
Dude. At the ripe old age of 16 I responded to a Craigslist ad, drove to a trailer park, handed over $39 and purchased a new-in-cosmoline Norinco SKS. $60 and a quick drive to the surplus store later and I had a 30-round mag and 1400 rounds of armor-piercing ammunition. Sixteen. Somewhere in a safe in a trailer park in a cul-de-sac in the middle of the desert of northern New Mexico, there's a form where I lied about my age to a dude selling assault rifles through the little nickel. 
You'll get no argument from me in regards to us having a shameful mental health system in the US. -Vastly underfunded and systematically whittled away to nothing in regards to care/hospitalization. I wonder, in another post @swedishbadgegirl@ pointed out gun/gun violence statistics in Sweden vs the US and it was night and day. Is this because Sweden has both less guns and better mental health care/screening? Also, you respond to the "waiting period" aspect but not to the types of guns comment. Do we need more than simple hand-guns/rifles/shotguns etc? If so, why?
Because the difference is purely cosmetic. Nobody is arguing for unrestrained possession of automatic weapons -- aka "machine guns." And the difference between your basic hunting rifle and what people refer to as "assault rifles" is simply a difference in stock, sight and magazine. Imma gonna hold my nose and, as much as I hate to, link to Fox News. Because even a broken clock is right sometimes, and this is one of Fox's moments: http://www.foxnews.com/politics/2013/01/16/gun-debate-what-makes-gun-assault-rifle/
If the difference is "purely cosmetic" why is it that nearly every state limits magazine capacity to five if you're hunting? Ever ripped through a 30-round mag with an AR-15? I have. It's hella faster than ripping through three ten-round mags. And that's when you give a shit about what you're shooting at, not doing the dumb-ass Rambo trigger finger trick. Peruse the North Hollywood Shootout for other "cosmetic" differences; those "cosmetic" differences are why the cops in my 'hood sport S&W 40s and Benelli M4s and AR-15s and body armor. So now, when somebody gets pulled over by the airport, they're covered by the same amount of firepower and the same attitude as Marine Recon in Baghdad. Which is hardly "cosmetic."The patrol officers were armed with standard Beretta 92F and Beretta 92FS 9mm pistols and Smith & Wesson Model 15 .38 caliber revolvers, while officers including James Zaboravan also carried a 12-gauge Ithaca Model 37 pump-action shotgun. The officers' weaponry could not penetrate aramid body armor worn by Phillips and Mătăsăreanu, which covered most of their bodies and provided more bullet resistance than standard-issue police Kevlar vests. The robbers' heads were the only vital organs that were unprotected, but most of the LAPD officers' service pistols had insufficient range and relatively poor accuracy. Additionally, the officers were pinned down by the heavy spray of gunfire coming from the robbers, making it difficult to attempt a headshot.