Crown prosecutor Ron Swanwick said police searched Mumford's home in the northern Brisbane suburb of Alderley on March 7, 2023.

Police examined Mumford's phone and found he had attempted to sell a 3D-printed replica submachine gun to five different people over 10 days using Facebook private messages.

Mr Swanwick said the firearm was less than 75 centimetres in length and had been built to fire .223 calibre bullets but was temporarily inoperable.

"On March 5 he offered to sell the replica for $10,000 and he sent a photo of him holding it," Mr Swanwick said.

The 3D-printing process involves using a digital design file and computer-controlled equipment to create a physical object typically by using hundreds of layers of molten plastic.

Judge Vicki Loury said she was concerned Mumford had refused to co-operate with police.

"What he hasn't done is to tell the police where these weapons came from. Somebody obviously has a file to print a replica submachine gun. Who is that person?" she said.

Defence barrister Francis Martin said none of the sales had gone ahead and Mumford was trying to source cash for drugs.

"Hopefully he has some future. He plans to do a bakery course and buy a home," Mr Martin said.

Judge Loury said Mumford's prior record for possessing a loaded pistol showed he had not been deterred from obtaining weapons.

Mumford was sentenced to four years' imprisonment with a mandatory minimum two-and-a-half years in custody for supplying shortened firearms.

Mumford will be eligible for parole in September 2025 due to already serving 429 days in custody.