Paul Davy, 43, was trying to get his former partner's dog back when he approached a home in Kendall on the NSW mid-north coast in November 2023.
An argument ensued and the father-of-one, who did not pose any risk, was fatally shot in the chest at close range.
Supreme Court Acting Justice Ian Harrison on Thursday jailed the gunman, Luke Willcockson, until at least 2040, calling the death "senseless, unprovoked and tragic".
"The events that give rise to these proceedings are yet another example of total and unqualified stupidity," Acting Justice Harrison said.
Willcockson wanted to plead guilty to manslaughter and gave evidence he did not know the firearm was loaded.
He told police he knew nothing about the firearm when questioned, although Justice Harrison called Willcockson's attempts to cover up his actions "inexplicably stupid".
In his own address to the court, Willcockson expressed deep condolences to Mr Davy's loved ones.
"I'm truly sorry for the pain, grief and suffering I have caused," he read.
"I never intended for Paul to be seriously hurt or lose his life."
The pair egged each other on in the moment before the murder, the court heard.
"Get the f**k out here ... or I'll burn your car in the street," Mr Davy reportedly said.
"You won't shoot me ... you don't have the balls to do it".
Justice Harrison did not accept Mr Davy posed a genuine threat, but noted the impromptu nature of the event.
"Mr Willcockson's offending was relatively spontaneous and unplanned," Justice Harrison said.
His sister, Dona Davy, spoke in court on Monday and laid bare the inescapable pain his murderer had caused the family.
She said her mother became frail almost overnight as a result of the "unspeakable loss of Paul".
In her own statement - read by the crown prosecutor on her behalf - his mother wrote that catching a glimpse of fishing rods was enough to reduce her to tears.
"You took my friend, my love, my singing and dancing partner, my fishing partner," his mother's statement read.
"It is so hard to even say his name without crying".
Arrested days after the shooting, Willcockson was found guilty of murder in February following a weeks-long jury trial.
He had earlier pleaded guilty to two counts of perverting the course of justice over flawed attempts to create a false alibi.
With time served, he will be eligible for parole in November 2040.
His full sentence will expire in May 2046.
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