A 2008 study on the effects of the firearm buybacks by Wang-Sheng Lee and Sandy Suardi of University of Melbourne and La Trobe University studied the data and concluded "the NFA did not have any large effects on reducing firearm homicide or suicide rates."[53]
In 2009 another paper from the Australian Institute for Suicide Research and Prevention at Griffith University also studied suicide in Queensland only. The said "No significant difference was found in the rate pre/post the introduction of the NFA in Queensland;

Subsequently, they compared the incidence of mass shootings in Australia and New Zealand. Data were standardised to a rate per 100,000 people, to control for differences in population size between the countries and mass shootings before and after 1996/1997 were compared between countries. That study found that in the period 1980–1996, both countries experienced mass shootings. The rate did not differ significantly between countries. Since 1996-1997, neither country has experienced a mass shooting event despite the continued availability of semi-automatic longarms in New Zealand. The authors conclude that "if civilian access to certain types of firearms explained the occurrence of mass shootings in Australia then New Zealand would have continued to experience mass shooting events."[45] In 2012, McPhedran and Baker found there was little evidence for any impacts of the gun laws on firearm suicide among people under 35 years of age, and suggest that the significant financial expenditure associated with Australia's firearms method restriction measures may not have had any impact on youth suicide.[46] Head of the New South Wales Bureau of Crime Statistics and Research, Don Weatherburn described the Baker and McPhedran article as "reputable" and "well-conducted" [47] Weatherburn noted the importance of actively policing illegal firearm trafficking and argued that there was little evidence that the new laws had helped in this regard.[48] He also stated that the 1996 legislation had little to no effect on violence saying the "laws did not result in any acceleration of the downward trend in gun homicide."

https://en.wikipedia.org/wiki/Gun_laws_in_Australia#Research