In support of John Lott's extensive research on guns in America (see his book "More Guns, Less Crime"... Web Link
it may be helpful to study the opposite "Less Guns, More Crime" from an Aussie policy...
The result after the Australian government instituted a $500 million gun buyback program... effective you ask???
Armed robberies rose significantly and home invasions rose as well.
Moreover, assaults involving guns rose more than a 25% and murders with a gun rose nearly 20%.
Note -- crime with guns increased after the gun ban was passed.