Gun registry only helps track the use of weapons that get put into hands of people legally using them. The problem with that is most of the guns used in crime are ferried north from the US along our very invisible border. But the obvious stuff need not be rehashed.
The only thing that will cut down on gun crimes is removing the element that creates it, the criminal. Over time humanity has devised many usefull ways of dealing with THAT element, however evolution now prohibits firing squads and public executions due to the utra soft mentality of progress and rehabilitation.
Forget the guns and start working on removing the hands that hold them. :
The registry hasn't reduced crime. And before this goes any further, you can repost your query in 'The Great Gun Control Debate', an mega thread on the subject. Where you will likely find your question already answered. This one is locked.