According to The Washington Times, a not-yet-published report commissioned by the National Institute of Justice concludes there's no solid evidence the federal "assault weapon" ban did anything to reduce gun violence or that failing to reauthorize the law, which expires September 13, would have a noticeable effect on crime. "We cannot clearly credit the ban with any of the nation's recent drop in gun violence," writes University of Pennsylvania criminologist Christopher Koper in the NIJ report. "Indeed, there has been no discernible reduction in the lethality and injuriousness of gun violence."
That conclusion is not terribly surprising, since the ban covers guns that were rarely used in crimes to begin with, based on criteria that have little to do with lethality. But it's significant coming from the NIJ, the Justice Department's research arm, which has a reputation for careful, dispassionate analysis.