Regarding Australia, there's an analysis here from 2006, 10.5 years after the gun law reforms:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2704353/
Here are the key points from the paper:
> A radical gun law reform occurred in Australia after a gun massacre (35 dead and 18 seriously injured) in April 1996. Semi‐automatic and pump‐action shotguns and rifles were banned; a tax‐funded firearm buyback and amnesties saw over 700 000 guns surrendered from an adult population of about 12 million.
> The total firearm deaths, firearm homicides and firearm suicides had been falling in the 18 years preceding the new gun laws. In all, 13 mass shootings were noticed in the 18 years preceding the new gun laws.
> In the 10.5 years after the gun law reforms, there have been no mass shootings, but accelerated declines in annual total gun deaths and firearm suicides and a non‐significant accelerated decline in firearm homicides. No substitution effects occurred for suicides or homicides.
edit: it is interesting that they looked for substitution effects. Like `sdenton4` commented, the lethality of the weapon matters.
If it is difficult to access firearms and there isn't really a similarly lethal alternative to easily kill someone else or yourself, it seems intuitively reasonable that we might expect to see less death.