My favorite study on this subject is the Harvard Law School study titled WOULD BANNING FIREARMS REDUCE MURDER AND SUICIDE?
It can be found at http://www.law.harvard.edu/students/orgs/jlpp/Vol30_No2_KatesMauseronline.pdf
It concludes as follows:
The burden of proof rests on the proponents of the more guns equal more death and fewer guns equal less death mantra, especially since they argue public policy ought to be based on that mantra.149 To bear that burden would at the very least require showing that a large number of nations with more guns have more death and that nations that have imposed stringent gun controls have achieved substantial reductions in criminal violence (or suicide). But those correlations are not observed when a large number of nations are compared across the world.