Have to work on those machete laws, I guess.
If you look at the data in sources like this, I can see no significant change in any crime trends around 1996.
Aside from a couple of peaks in 1991, 1992 and 1997, robberies with a firearm (Tables A1 and A2) have held fairly steady until they began dropping in 2004. Whether there was another change in the laws at that time, I don't know.
You can look at Figure 4, too, and draw whatever conclusions you think you can.
I personally think the Australian crime rate in general is running on different drivers than just the availability of guns.