"Just Ban Them"

Fully automatic weapons, to include assault rifles (which hadn't been invented yet), were banned by the Firearms Act of 1934. Of course, criminals still managed to get them, but for sale to law-abiding civilians, manufacturers started making semiautomatic variants. 

In 1993, Congress passed the "Assault Weapons" Ban. I use quotation marks because there's no such thing as an assault weapon in the firearms lexicon. It's an arbitrary legal term that can be defined rather accurately as "scary-looking guns." A gun was defined as an "assault weapon" if it had at least two features from a list that were largely cosmetic and had no effect on lethality, e g. a vertical "pistol" grip on a rifle, or a barrel shroud to prevent a shooter from accidentally burning himself by touching a hot barrel after shooting.

Unsurprisingly, studies showed that removing these features had no effect whatsoever on gun violence, and the bill was allowed to sunset 10 years later. However, some states adopted their own versions. Connecticut copied it verbatim, sans sunset clause.

So, when Adam Lanza's mother bought the rifle he would later murder her for, she was limited to the ban-compliant Bushmaster XM15-E2S. When Adam killed her, 6 other adults, and 20 small children, it proved to be just as lethal despite not having a bayonet lug or collapsible (read: adjustable for users of different heights) stock. Incidentally, Adam Lanza tried to buy a rifle a week before the shooting, but failed a background check. Amazing how he got one through other means, since he obviously held the law (and the sanctity of life, for that matter) in such high regard.

Connecticut responded by banning guns with one feature from the list instead of two. They also banned a number of guns by name, but of course many people are grandfathered in, so you can still get one if you want it as badly as Adam did. They also banned "high capacity" magazines. I use quotation marks this time because engineers, not politicians, design weapons to hold a certain amount of ammunition. If Eugene Stoner designed the AR-15 to accept 20- and 30- round magazines, that makes them standard capacity. Very few, typically large caliber or high-powered, guns were designed to hold the arbitrary ten or fewer.

I digress. Adam Lanza and his 30-round mags were still less lethal than Seung-Hui Cho, who killed 33 people at Virginia Tech. He used only handguns with low capacity magazines. He changed magazines at least 17 times. This can be accomplished in 1-2 seconds with a bit of practice, and a second gun is even faster. A magazine ban wouldn't have affected him. He did trap victims and delay police by securing doors with chains and padlocks, so I guess banning those might have saved a few people.

California went a step further and mandated that weapons sold there require a tool to change magazines. This feature was present on the guns used in San Bernardino.

Now, the 1993 federal assault weapons ban is being proposed for reinstatement, although we have observed and studied its ineffectiveness. That demonstrates clearly that its proponents are either supporting feel-good measures that they know will not work, or haven't done any research on the matter. I'm not sure which is worse.

All the above laws did nothing to prevent the next shooting, but subsequent shootings have served as catalysts to pass more restrictions. "Common sense" is that gun control doesn't work. "Common sense" is that when the next law is passed, there will be another shooting, and another law. That's not a fallacy. The slope is real. They know damn well that nothing will work until civilians can't have guns. Then we can be just like Paris.