The New Zealand gun buy back ends today. The very fact that semi-automatic weapons are now prohibited and the buyback took place is a success. Politicians, supported by 70% of the public, are changing the direction of travel for New Zealand gun culture. This country had climbed to an estimated 17th highest number of guns per capita in the world. Three decades of plaintive warnings about the need to ban semi-assault rifles before another massacre took place, had no effect.

The primary aim of the buyback is prevention of future mass killings by taking these guns out of society and compensating the previous owners. Prevention is a poor servant and a hard master.

Huge political capital and up to NZ$200m (US$130m) are being spent by government in return for a success that will be revealed by an absence of negative events, by continued safety and trust within communities and other intangible benefits.

Buybacks have been shown to work when they are part of a package of measures and the arms bill, currently going through parliament, is an important part of that package. Police commitment to the often invisible work of building trust and de-escalation of conflict without themselves using firearms will be crucial.

Domestic violence prevention is also important as mass killings often start in the home. A secret service report in the United States also found that most school shooters had been victims of bullying and had a history of disciplinary problems.

Most gun buybacks are small and local and take in in fewer than 1000 firearms, compared to an estimated 300m small arms worldwide in the hands of civilians. Such small buy backs do not make a difference to violent crime or suicides but Los Angeles police, among others, continue to run them year after year. This is because they empower local people to support gun control and give hope to their communities.

National buybacks in Argentina and Brazil during the 2000s included new laws and research suggests firearms-related mortality and thefts were reduced.

The Australian buy back following the 1996 Port Arthur massacre remains the world’s leading example. It is estimated that 20% of Australian guns were handed in and destroyed. This was followed by a National Firearms Agreement, which introduced major new restrictions on gun ownership, including setting up gun registers in all states.

Harvard researchers concluded that the measures had been “incredibly successful in terms of lives saved”, including gun suicides and homicides. A massacre is generally defined as an event in which four or more people are killed, excluding the shooter. There were 13 mass shootings in Australia in the 18 years before Port Arthur; in the 22 years since, there has only been one.

The word “estimated” is important. Most attempts to assess the success of the New Zealand buyback focus on the supposed number of firearms and the percentage of this figure handed in. This is a furphy – in planning the buyback, the government spent good money on KPMG estimates that were based on estimates made 20 years earlier by Judge Thorp. His estimates were based on estimates from the gun register which police abandoned in the 1970s because the level of accuracy was so poor.

There has been a register of military-style semi-automatics and this included around 15,000 weapons. Police will know if all of these have been handed in, but the buyback includes a wider range of semi-automatics.

Some in the pro-gun lobby seized on a recent police data breach as a reason to repeat threats they won’t hand in their guns. Ordinary gun owners have been increasingly unhappy in recent years with police arms administration and this gaffe undermines the careful support work by police during the actual gun handovers.

Even so gun owners who refuse to hand in their now illegal guns may merely alienate the rest of New Zealand and they expose themselves to prosecution. As soon as the buyback was announced, online gun extremists were debating burying guns or otherwise concealing them from police.

Gun advocates insist that all licensed firearms owners are law-abiding citizens – they just won’t be obeying this law. History suggests however that changing the law is a very effective approach to changing behaviour. This will not happen at once and it won’t happen overnight.

But, looking back, it is highly probable the buyback will be seen as the beginning of real change toward a gun culture that supports a safe and peaceful New Zealand.

Hera Cook is a historian and a public health researcher at the Otago University Wellington Medical School, and a team member at the pressure group Gun Control NZ