http://www.gq.com/story/new-gun-control-study
Massive New Study Shows How Effective Gun Control Can Be

A few months ago, I went to Los Angeles's beautiful Arclight Cinemas in Hollywood to see a midnight screening of Star Wars: The Force Awakens. I had never seen the lobby so crowded. There were more than thirty separate sold-out or near sold-out screenings of the movie happening that evening. Every single screen was dedicated to the return of the legendary franchise, and the crowd seemed impossible to navigate through. People were so happy and excited. It was the kind of night that you dream of if you love going to the movies. But, as much as I wanted to just enjoy it, I couldn't shake a low-level, but constantly nagging sense of dread. "This would be the type of event that a gunman would want to destroy," my brain kept whispering to me. It felt like our very happiness was dangerous, and somehow made us targets. That at any moment there was a real possibility that a damaged person with a gun could end our fun.
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The study, which was published by Epidemiologic Reviews, looked at gun laws around the world and the gun violence stats both before and after those gun laws were enacted. The results? Well, while the academics are quick to say that the study doesn't conclusively prove that gun control reduces gun-related homicides, it does show that there is a trend whereby an increase in restrictions on firearm purchase and ownership leads to a decrease in gun deaths. So even though the evidence might not "prove" that gun control reduces deaths, the evidence does strongly suggest that.
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Here's how Vox characterizes the findings.

"Rather, countries passed big packages of gun laws, which overhauled the nation's firearm code fairly broadly, which all tended to share similar features. According to [lead author Julian] Santaella-Tenorio, they generally included:

Banning "weapons that are actually very powerful," like automatic weapons.
"They all implemented background checks."
"They all required permits and licenses for purchasing guns."
South Africa's comprehensive Firearm Control Act, passed in 2000, contained all these measures. One study found that firearm homicides in five major South African cities decreased by 13.6 percent per year for the next five years."
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By contrast, laws favored by the National Rifle Association (such as concealed carry or stand your ground), when implemented, either had no effect on gun deaths or increased gun violence. And Santaella-Tenorio found this by considering not just studies that reached this conclusion, but also studies that supported loosening gun laws.

Most of the studies that supported these laws were written by a handful of authors, like Florida State's Gary Kleck and independent scholar/Fox News columnist John Lott. Scholars who reexamined their conclusions, sometimes even using their own data, generally came to the opposite results.

The point, then, is that the pro-gun studies tended to be outliers in the literature, and were not supported by the most rigorous available analysis.