According to the CDC, firearms-related homicides numbered 11,101 in 2011. Of those, about 4% involved rifles of any kind, with 2% or less being semi-automatic "assault" rifles.
Following Australia's lead in banning the ownership of such rifles isn't going to reduce firearms-related homicides by any meaningful number. In 2011, mass shootings accounted for 0.16% of all firearms-related homicides.
In 2004, after studying 10 years of the effects of the Federal Assault Weapons Ban, the Department Of Justice had this to say:
Should it be renewed, the ban’s effects on gun violence are likely to be small at best and perhaps too small for reliable measurement. Assault weapons were rarely used in gun crimes even before the ban.
When people say an "assault weapons" ban is a good place to start, I have to wonder what drove them to that conclusion? It wasn't the data, which shows such legislation is entirely a feel-good measure that sweeps 98% of gun crime under the rug.
Nor was it bipartisan support. Polls from Pew, Gallup, and other organizations after the shootings in Aurora, CO and Newtown, CT show the public is split within the margin of error for/against more gun control.
On the other hand, I think there would be widespread support on both sides of the aisle for reforms addressing mental health and our culture of violence.
Couple that with the fact that any major gun control bill will have long-odds overcoming a 33-seat GOP majority in the House of Representatives, and I don't see why people insist on starting with a nonstarter.
If more firearms legislation (ineffective or otherwise) is really your goal, your best near-term option would be an Executive Order from President Obama. Barring that, it would require working towards a Democrat-controlled Senate and House in 2014, giving us the same political environment that Clinton had when he signed the Brady Bill and Federal Assault Weapons Ban during his first term.