Will Oremus explains Australia's sweeping 1996 gun control law, which banned semi-automatic and automatic firearms after a mass shooting in Tasmania that resulted in 35 deaths and 23 injuries:
At the heart of the push was a massive buyback of more than 600,000 semi-automatic shotguns and rifles, or about one-fifth of all firearms in circulation in Australia. The country’s new gun laws prohibited private sales, required that all weapons be individually registered to their owners, and required that gun buyers present a “genuine reason” for needing each weapon at the time of the purchase. (Self-defense did not count.) In the wake of the tragedy, polls showed public support for these measures at upwards of 90 percent.
Dylan Mathews goes through the available research on the law's effects:
It seems reasonably clear [that] the gun buyback led to a large decline in suicides, and weaker but real evidence that it reduced homicides as well. Such a buyback isn’t in the cards in the U.S. anytime soon — an equivalent buyback here would entail the destruction of 40 million guns …