Street police say dangerously erratic criminals under the influence of the drug crystal methamphetamine hydrochloride – or ice – are convinced they are being followed and are carrying handguns for "protection".

The armed crime taskforce has been assigned to uncover the sources of a booming business in illegal firearms, with reports of farmers and registered gun collectors robbed by specialist burglary teams.

"This is a key priority for us," Assistant Commissioner (Crime) Steve Fontana said.

Specialist police squads say they regularly find heavy-calibre weapons during raids on suspects.

Senior police say even when the guns are seized criminal groups seem to have little trouble re-arming within days.

Mr Fontana told Fairfax Media crime groups were breaking into regional properties looking for guns. "We believe these are targeted crimes where the offenders know there are firearms in the houses," he said.

Registered firearm collectors had been robbed, with burglars grabbing up to 12 guns in one raid, Mr Fontana said.

"This is a real concern for us. Nearly every day our members are pulling up cars and finding loaded firearms in the vehicles.

"Once guns seemed to be in the hands of organised crime groups but there has been a trickle-down effect. Many lower-level crooks now want to be armed."

The Assistant Commissioner said firearms had become an illegal currency in drug deals. "We do know of cases where guns have been used as payment for ice."

In 2012, the Australian Crime Commission estimated there were 250,00 long-arm firearms and 10,000 hand guns in the illicit market.

Police also believe criminals are using friends and relatives with clean records to apply for firearm licences to stockpile weapons.

Mr Fontana said police were also worried about the growing trend of criminals shooting at properties to intimidate the occupants – regardless of who is present at the time. In one case, more than 70 shots were fired from military-grade guns. "These bullets can travel hundreds of metres and cut through metal."

Earlier this month, a father of three was shot dead outside an Epping home when at least one man opened fire on the house and a car.

Police say Ben Monteath, 39, of Doreen was visiting the house after a children's party and was shot when he went to investigate the source of several gunshots.

Police believe he may not have been the target of the attack. He was shot in the chest and died at the scene in Plowman Road.

Jermersel Selimovski, 48, also of Doreen, has been charged with murder but police are still hunting two men suspected of being in the shooting party.

"We are seeking associates of the accused who may be involved," the head of the homicide squad, Detective Inspector John Potter, said. In another case, a Thomastown family has been the victim of five shooting attacks in the past seven months. One house in Chateau Court has been blasted three times, a Mill Park property once and the family business has also been attacked.

Anyone with information should contact Crime Stoppers on 1800 333 000.