A video game fan who 3D-printed replica guns for use in costumes has been given a 12-month suspended sentence in the NSW District Court.

Sicen Sun, 28, was arrested in February 2017 after he advertised one of his imitation weapons for sale for "$1 million negotiable" on a Facebook buy, swap and sell group for military items.

Sicen Sun received a 12-month suspended sentence after using a 3D printer to make replica firearms.

The post was taken down three days later, however the Firearms Squad launched an investigation.

Sun, then an advertising consultant, described himself to police as a "cosplay enthusiast" whose hobby of dressing up in costumes got "out of hand in regards to making the firearms appear as realistic as possible".

He made multiple replica guns on his 3D printer after initially searching online for plans to make a firearm used in the videogame Halo. None were capable of being loaded or fired.

At his sentencing hearing, Sun said he thought making realistic props was in a legal "grey area", and he realised now "how silly, idiotic, stupid and naive my actions were".

On Tuesday, Judge Penelope Wass sentenced Sun to a total of 12 months imprisonment, which was immediately suspended, and instructed him to enter into a good behaviour bond.

Sicen Sun was given a 12-month suspended sentence. AAP

He received a conviction with no further penalty for advertising the replica gun online.

Judge Wass said Sun's offending posed only a "very slight" risk to public safety, and the weapons he produced were among "the least dangerous" contemplated by legislation.

"They were being used in fantasy role-play games," Judge Wass said.

The court heard Sun, a journalism graduate from the University of Technology Sydney, first developed an interest in videogames when he worked at an internet cafe in 2007.

In 2015, when his parents were deported to China, his interest became "obsessive" and he began to make video game props and costumes to fill what he described as a void in his life.

Judge Wass said when Sun posted the replica SIG Sauer P250 pistol on Facebook, it was likely because he was "compelled" to have his work as a craftsman acknowledged.

"I accept, particularly given the sale price offered, that it was never his intention to sell the item," Judge Wass said.

The court heard Sun has been diagnosed with adjustment disorder and anxiety and is a low risk of reoffending.

"He is now all too aware of the consequences of possessing replica weapons," Judge Wass said.

Speaking outside court, Sun's lawyer said his client was "very relieved" and pleased with the outcome.

Surrounded by cameras, Sun was asked if he had any advice for others who might want to 3D-print guns.

"Don't do it," he said.

The replica firearms will be destroyed by police.