The NFA is famous for banning semiautomatic long guns (including the ones used by the Port Arthur shooter), but, as Webster points out, it also made buying other guns a lot harder too. People have to document a "genuine need," pass a safety test, wait a minimum of 28 days, have no restraining orders for violence and demonstrate good moral character, among other restrictions, Webster writes.

"In Australia, they look at someone's full record and ask, 'Is this a good idea to let this person have a firearm?'" Webster says. In the United States, "we do pretty much the opposite. The burden is on the government to show that you are too dangerous to have a firearm."

Australia also initiated a mandatory gun buyback program in 1996, leading to the purchase and destruction of more than 650,000 semiautomatic and pump-action rifles and shotguns.