Australia radically changed its firearms laws following a mass shooting in Tasmania in 1996 (The Port Arthur Massacre)
The below link is to a paper recently done by the Australian Institute of Criminology:
www.aic.gov.au/documents/7/D/5/%7B7D52BA73-81EC-42F7-8246-468FB222FB4B%7Drpp116.pdf
By suddenly restricting ownership of large swathes of previously legitimately held firearms, you end with a 'grey market' - I quote:
"The grey market consists of all long-arms that were not registered, or surrendered as required during the gun buybacks, following the National Firearms Agreement (1996). Grey market firearms are not owned, used or
conveyed for criminal purposes but may end up in the illicit market."
(, Fri 20 Jul 2012, 15:05, Reply)