Detective Senior Sergeant Steve Wescott said police were making good progress on the investigation.
"No one should have to put up with this activity in their neighbourhood and we will continue to target those involved in violent offending."
They would be unable to provide further information about the firearm, police said.
Anyone who had witnessed or heard anything suspicious early on December 20 who has not yet spoken to police is asked to do so on 105, quoting file number 201220/8063.