From the linked study..........
In the synthetic control approach that compared the overall homicide trends in Australia pre- and post-NFA with trends from 28 other countries aggregated and weighted to create a counterfactual condition, Bartos et al. (2020) found that the reduction in overall homicide experienced by Australia was about 50 percent larger than would have been expected had Australia not enacted the NFA, although the greatest decline (and deviation in total homicide rates between Australia and the synthetic control) occurred not in 1996 but in 2002, which coincides with the passage of the National Handgun Control Agreement in Australia.