"An examination of the effects of concealed weapons laws and assault weapons bans on state-level murder rates." Mark Gius. Applied Economics Letters. DOI: 10.1080/13504851.2013.854294

Read more at: http://phys.org/news/2014-01-restric...lated.html#jCp

This has been discussed previously but without access to the actual paper. It is quite short at four pages only, 107 KB