Here's homicide rates over time (clearly showing the spikes I was talking about):
http://theconversation.com/three-charts-on-australias-declining-homicide-rates-79654
Compared to other countries, Australia's homicide rate spiked twice since their gun buyback program. Meanwhile, countries like the US saw much faster homicide rate declines.
When homicide rates were already declining before their gun buyback program, how can any study claim, with any seriousness, that Australia's gun buyback program was effective?