Twenty-one years ago, Martin Bryant shot and killed 35 people and wounded 23 others using a semi-automatic weapon in and around Port Arthur in Tasmania.

Just 12 days after the massacre, state and federal governments united to enact uniform gun control laws.

That initiative remains one of then Prime Minister John Howard's greatest legacies.

But now anti-gun advocates are becoming increasingly concerned that Australia's world-renowned gun control measures are being significantly weakened.

They want an audit of the weapons in circulation to establish just how widely available guns are in Australia these days.

Editor's Note: During this interview, it was stated that the former Howard government had banned all automatic and semi-automatic weapons. RN Breakfast acknowledges the 1996 National Firearms Agreement banned military style automatic and semi-automatic firearms, while limiting the availability of non-military style semi-automatic rifles and shotguns to primary producers, professional vermin exterminators and a limited class of clay target firearm users.