Police Minister Judith Collins says the Government is looking seriously at legislation to restrict the sale of powerful air rifles which are being blamed for two slayings in Auckland.

Police Sergeant Don Wilkinson died after he was shot with an FX Monsoon airgun while on an undercover drugs operation in 2008.

And now it has been revealed that the same type of weapon was used in the slaying of Keith Kahi, 44, in the eastern Auckland suburb of Botany Downs nine days ago.

Earlier this year, after John Skinner was found guilty of Mr Wilkinson's murder, police said licensing powerful air rifles as firearms needed to be addressed quickly.

Police Commissioner Howard Broad said a proposal to reclassify air rifles was considered before Mr Wilkinson's death and was before Parliament. Under existing law anyone over 18 can buy an air rifle, including the powerful FX Monsoon or similar air rifles, without a firearms licence.

The Police Association said the guns were weapons of choice among criminals who knew they would not be arrested if they were found with them. The guns were killers in the wrong hands and the law needed to be changed, said the association.

A bill to restrict the sale of the weapons had been before Parliament since 2005 but had not passed into law.

Mrs Collins said yesterday it was a complex and technical issue and work being done by police on a change in the law was due to be put before her in the next week or so.

She told Radio New Zealand yesterday technology had moved on since the original bill was introduced.

She said it was clear the old BB gun, which was used by many people to learn to handle firearms safety, was vastly different from modern, gas-powered air rifles.

She said any change to the law would have to go through Parliament but it would be an "interesting" move to ban them when other powerful weapons were available for hunters.

Muzzle energy is a measure of a bullet's power, expressed in foot-pounds. One ft-lb is the energy exerted on impact by a 1lb object falling one foot.

* Calibre: .177
* Muzzle energy: 15ft-lb

FX Monsoon
* Calibre: .22
* Muzzle energy:30ft-lb

.22 rifle
* Calibre: .22LR
* Muzzle energy: 100 to 130ft-lb

* Calibre: 9mm
* Muzzle energy:200 to 400ft-lb

M16 rifle
* Calibre: 5.56mm Nato
* Muzzle energy:1300ft-lb

Sources: Nato, US Army, airgundepot.com, beemans.net