In Australia, in 1996, Martin Bryant shot and killed 35 people with a Colt AR-15 5.56mm semi-automatic assault rifle and an L1A1 semi-automatic 7.62mm SLR.

That led to the gun buyback scheme that took more than 700,000 guns out of private hands. Gun numbers have crept back up and are now more than they were pre-buyback. (I am using the popular term ''gun'' although I was told when I joined the army that guns were what the artillery used, and that the correct terms are firearms or small arms.)

I have always had a healthy respect for guns. When I was in primary and secondary schools in Malaya during the Malayan Emergency I used to spend afternoons ''helping'' Sergeant Hague, the battalion armourer, to repair and maintain the full range of weapons used by my father's Gurkha battalion. Sometimes an exotic captured weapon would come in, like a Thompson submachine gun that I learned to strip down and operate. On the firing range I got to fire off thousands of rounds of ammunition that were nearing their use-by date. In those days, my father always had a pistol at home or in the car because of the threat situation. The pistol had to be readily accessible and my father was very strict about weapon safety. When I joined the Australian Army there were similar strict rules about the safeguarding and handling of our issue L1A1s that we kept in our rooms.

The first guns I personally owned were an automatic AR-15 (M16) and a Colt .45 pistol. I was a platoon commander in South Vietnam at the time and platoon commanders were issued with the Owen submachine gun, a clunky, heavy and rust-prone World War II-vintage weapon, for which the army issued us 1944-era ammunition. I bought both weapons from the 173d Airborne hospital for $30 each after they had been helicoptered back with dead GIs. The Australian Army at the time had only bought enough M16s to provide them to section commanders and forward scouts. Pistols were provided only to company commanders. So like many others, I bought my own weapons. My reasons for having them were essentially practical - the M16 was light and a much better weapon than the Owen, and the pistol was easier to carry around our base area.

Something particularly noticeable to us was the Americans' preparedness to use lots of ammunition, facilitated by the fact that all of their firearms could fire on automatic. This included the concept of ''reconnaissance by fire'' and everyone firing a full magazine outwards from a harbour position at last light. Neither seemed to us to be very effective, particularly since the latter tended to give the harbour position away to the enemy who would then lob in mortar rounds.

Later in the 1970s, when working in Arizona, I bought a 9mm Colt pistol like my work colleagues, essentially for protection when camping in remote areas of the southwest, where there seemed to be lots of loony people with firearms. However, probably the most dangerous area I worked in for any length of time was Washington DC in the early 1990s, where there were far more than 400 gun homicides a year in a city of 600,000 people. They were mostly black-on-black and drug-related, but I often had to drive through the more dangerous parts of town to get from the embassy to the navy yard. On one occasion a young black guy I had inadvertently cut off, drew alongside my car and pointed a pistol at my head. Fortunately in the process he ran into the back of the car in front of him and, needless to say, I left them to it.

I can therefore understand the American desire to have a gun for protection - and they are selling in record numbers since the Sandy Hook massacre. The problems are the types of guns available and who can access them and for what purpose. I work in the US every year and usually go to local gun shows out of interest. In 2008 I saw a new AR-50 12.7mm sniper rifle with telescopic sights at a gun show in Elk City, Oklahoma for $3400 negotiable.

That weapon, with an effective range of 2400 metres, has no real place outside a war zone. The only form of identification required to buy it was my Australian driver's licence. At other times I have seen automatic weapons for sale, as well as 40mm M79 grenade launchers and the explosive grenades they launch.

In Arizona I have seen military assault weapons for sale at trash and treasure markets, including a Vietnam-era AK-47 which can fire 600 7.62mm rounds a minute. In Florida, in 2002, I was invited by a local gun shop to take part in their annual Fourth of July machine gun promotion. The aim was to detonate car wrecks filled with explosives.

In 1994, then-president Bill Clinton signed into law a ban on assault weapons manufactured after 1994, but the ban expired in 2004. It is possible the President might try to resurrect something similar. However there are now 260 million guns in the US, accounting for more than 9000 gun homicides a year. Realistically, the prospect of keeping semi-automatic assault rifles out of the hands of unstable people is going to be extremely low.

An Australian-style buyback scheme would simply be political suicide for Republican politicians in America given the enduring influence of the National Rifle Association. The more likely long-term outcome is better protection for schools and students. This could include permanent armed guards, metal detectors on entry, and having some staff trained to provide a fast reaction response - similar to the armed pilot scheme on US passenger flights. The idea of parents responding with firearms would be a nightmare scenario; in 2004, frantic trigger-happy parents responding to the Russian Beslan School hostage situation were responsible for many of the 385 deaths.

Clive Williams is an adjunct professor at Macquarie University's centre for policing, intelligence and counter terrorism, and a visiting professor at the Australian National University's Australian centre for military and security law.