Police who searched Aaron James Graham's vehicle also allegedly found a hooded jumper with a logo that read: "I will associate with whoever I want" and "bad laws", "good bikies".

Mr Graham, 24, was charged for illegally possessing the sawn-off shotgun and ammunition after officers from ACT Policing's anti-bikie Taskforce Nemesis stormed three homes in raids across the capital on Wednesday.

Police said in court they seized shotguns, assault rifles and a hand grenade among a weapons cache discovered in the roof of a Richardson house - a discovery a magistrate described as "frightening".

Two of the firearms found at that house were believed to be similar to those used to pepper a Waramanga house with bullets in July, a police officer told the ACT Magistrates Court on Thursday.

Mr Graham did not enter pleas and prosecutors, who said he was an associate of the Nomads, opposed his bail application.

Detective Senior Constable Stewart Alexander said they found weapons including a pump-action shotgun, two assault rifles, a double-barrell shotgun, modified pistol, hand grenade, firearm carry bags and assorted ammunition.

The court heard Mr Graham, who lives in Richardson, had been seen at the house where the weapons were found that night.

Court documents said police later searched a Monash property and looked inside Mr Graham's work ute, where they found the loaded sawn-off shotgun on the floor of the front passenger side seat, 21 shotgun cartridges and the jumper.

Detective Senior Constable Alexander said Mr Graham hadn't told police why he had the gun or what he planned to use it for, and said he likely had access to more firearms given his links to the Richardson house.

He said forensic tests would determine whether assault rifles found at the property were connected to the Waramanga shooting.

Prosecutors argued the discovery of the loaded firearm, as well as Mr Graham's links to the Richardson property, indicated there was a significant risk he would reoffend and it was a matter of community safety.

But his defence lawyer, Peter Woodhouse, said there was a presumption for bail in Mr Graham's matter, he had cooperated with police and he had no relevant criminal history.

He said there was nothing in his behaviour or record to suggest he posed a risk of reoffending or destroying evidence, and apart from visiting the Richardson property there was nothing else to link him to weapons allegedly found there.

Magistrate Karen Fryar said the matter was "difficult" but the likelihood of Mr Graham reoffending, from the information before the court, was not sufficient to refuse bail.

She later noted the alleged weapons cache was "very concerning" but said she would grant Mr Graham bail on strict conditions.

"I agree the Richardson scenario is frightening as a member of the community," she said.

He would be required to report to police three times a week, avoid the Richardson property where the weapons were allegedly found, and not contact 23 people police said had links to the Nomads.

Mr Graham's case returns to court on November 23.

Police also arrested a Chisholm man, 24, in the raids. He was summonsed to face court at a later date for possessing ammunition.