There could be a drop in the number of gun owners thanks to the Government's buyback scheme.

The Christchurch massacre has led to an overhaul of gun laws, with military-style semi-automatics and assault weapons now illegal.

Mary Vriniotis, from the Harvard Injury Control Research Centre, has studied the 1996 Port Arthur Massacre in Australia.

She told Kate Hawkesby gun ownership in Australia has dropped since the law changes.

"These measures have been estimated to reduce the number of guns in private hands by about 20 per cent, and to reduce the overall number of gun-owning househoolds in Australia by about 50 per cent."

Vriniotis said Australia hasn't had a mass shooting since, which shows that the scheme is working.

"In the 20 years before the law was implemented, Australia suffered about 13 mass shootings but in the 20 years after the law took effect there was no mass shootings apart from one family related incident."

"There was an immediate and lasting reduction in firearm homicides and suicides since that time."

She said the buyback scheme was the key to Australia's success.