The court heard that Ganderton was subject of a police search at a Merricks Rd address in Pyes Pa on December 12 last year undertaken under the Search and Surveillance Act.
When police searched his Ford Ranger they found the shotgun and 16 rounds of 12-gauge shotgun cartridges.
Ganderton, who is not the holder of a current firearms licence, told the police he used the shotgun for pig hunting. He had previously appeared before courts.
A fact not lost on Judge Thomas Ingram after he took the guilty pleas from Ganderton, who chose to represent himself in court.
Judge Ingram called for a pre-sentence report including home detention and community detention annexes.
But the judge told Ganderton not to underestimate the gravity of his offending.
"You have been here plenty of times before Mr Ganderton, so you know the score.
"I'm prepared to look at the possibility of home detention and community detention but you need to know that you're highly likely to get a prison sentence," he said.
"In the last three weeks sitting on the bench in Tauranga and Whakatāne courts, I have dealt with cases of unlawful possession of firearms on a daily basis.
"When I first came to Tauranga 15 years ago we were only seeing two or three cases a year, now it's become an everyday occurrence.
"People need to understand this will not be tolerated and people can expect serious sentences, with the real possibility of doing prison time," he said.
Judge Ingram remanded Ganderton on bail pending sentencing on April 23.
Ganderton was one of the seven people scheduled to appear in one of the Tauranga courts yesterday on charges of unlawful possession of firearms.
This included a 19-year-old Te Puke man, who pleaded not guilty to a joint charge of unlawful possession of a 9mm pistol in the Tauranga Community Magistrate's Court.
