SYDNEY, Australia -- It is for Americans and their elected representatives to determine the right response to President Obama’s proposals on gun control. I wouldn’t presume to lecture Americans on the subject. I can, however, describe what I, as prime minister of Australia, did to curb gun violence following a horrific massacre 17 years ago in the hope that it will contribute constructively to the debate in the United States. I was elected prime minister in early 1996, leading a center-right coalition. Virtually every nonurban electoral district in the country — where gun ownership was higher than elsewhere — sent...