Judge Collins sentenced him to prison for two years and three months. Kani has already been in custody for 77 days on remand.
Defence counsel Philip Ross said that Kani, who has the word "Dogwar" tattooed across his forehead, had handed in his Mongrel Mob patch and wanted "a different life for himself".
Judge Collins replied by asking, "Is it unfair to be cynical?" He said that sentencing days in court must be causing a big drop in gang membership.
"I don't have any problem at all with people belonging to the Mongrel Mob. What I have a problem with is people offending," Judge Collins said.
"The best outcome for everyone would be a change in (gang) philosophy, so that young men like you don't end up where you are today having to listen to someone like me send you to jail."
The judge said that the weapons found in Kani's possession were a cut-down shotgun and two modified .22 firearms, one found with a suppressor and a loaded magazine.
The judge said that "we're in territory where that becomes serious offending", when gang members are found with cut-down weapons.
Guns in the hands of gang members were a matter of huge concern at the moment, he said.
"That concern has never been more acute than it is now," the judge said.
Judge Collins sentenced Kani to 27 months in prison for having the loaded firearm with a suppressor, 18 months concurrently for the other weapons and one month on the drugs charge. He convicted and discharged him for possessing the ammunition.
The judge noted that Kani was fluent in te reo Māori.
"That's impressive," he said. "It's always impressive when someone can speak in two languages. It means you can think in two languages."
