Mr Wilson, 29, is an anarchist once named one of the most dangerous men in the world because of his attempts to disseminate information showing how to make a printable and untraceable gun.

NSW is the only state in Australia where it is an offence - punishable by 14 years imprisonment - to possess a digital blueprint to make a 3D gun. The 2015 legislation bans storage in the cloud, on a computer, mobile phone or storage device, within or outside NSW.

Last week 27-year-old Sicen Sun, a gaming enthusiast, was the first person to be charged under this legislation after he allegedly attempted to sell an imitation 3D printed Glock pistol for $1 million. Police allege they found a range of imitation weapons in his Waverley unit.

Mr Wilson, 29, said "many thousands of Australians" had downloaded his instructions, and the nation was among the top 10 countries for downloads.

His site provides instructions on how to make parts for the Liberator pistol, which was tested by NSW Police firearms experts in 2013. As police fired the gun, it cracked open.

NSW Police ballistics expert Chief Inspector Wayne Hoffman told Fairfax Media on Friday that printed guns were so dangerous to victims and to those firing them that it was "not worth going there".

Using a cheap printer from Officeworks, police took 36 hours to print the gun.

Following the instructions was difficult for technical experts: "It wasn't like IKEA: step one, step two ..."

"We made them, they blew up on us, and the directions do warn of that," said Inspector Hoffman, adding the technology hadn't improved much since then.

To kill or injure someone, you had to get up very close. "Then you could seriously injure or kill them, but you could also kill yourself or have self inflicted injuries," he said.

When asked about the weapons allegedly made by Mr Sun, Mr Wilson said via email that the "components could not have possibly been useful for building working weapons". He said they were made from blueprints provided by one of the many other sites across the world.

While convincing imitations, it is understood that Mr Sun's alleged weapons were unable to be fired.

But Detective Superintendent Michael Plotecki, the firearms squad commander with the NSW state crime command, said imitation guns could be used to threaten or intimidate someone. He said state and federal police were working together to tackle the problem of downloaded blueprints.

3D printers have been used to to make chocolates, houses, prototypes of body parts including ears, and toys (such as blocks that resemble Lego).

Mr Wilson doubted whether 3D printing would supersede other technologies like CNC (computer numerical control) milling where computers control lathes and other machinery used to fabricate gun parts.

University of Wollongong 3D expert Thomas Birtchnell said 3D printing technology couldn't readily produce weapons, but it could help rogue gunsmiths create plastic gun parts or to create prototypes for metal guns.

Home CNC milling machines were now becoming more affordable and accessible to consumers, Dr Birtchnell said.

And if industrial 3D printers were to get into illicit hands they could also pose a threat.

"If 3D printers are set to become a part of our lives then there will be tension between the freedom to print the objects we desire and the ease with which this will be possible, affordable and legally permissible," Dr Birtchnell said.

Mr Wilson said Australians were "unfortunate" because they had no legal protections against their "government's adventures in censorship, surveillance and expropriation".

As an American, his right to carry arms was enshrined in the Second Amendment: "That Australia has nothing similar is a spiritual degradation unworthy of your history. Consider the English Bill of Rights. A poor Anglo farmer in the 17th century had more dignity than the modern Australian."