Christopher West told a psychologist he "just lost his shit" on the afternoon of April 9 last year, prompting he and a friend, Joshua Williams, to take extreme action.

Court documents said the pair pulled up outside the woman's Northcliffe Drive house in a stolen Toyota Rav 4 and began abusing and threatening her and her family members when she exited the house.

"Youse [sic] are all f--king dogs and your family's gone," he yelled through the car window.

"I'm going to f--king start shooting, I'm going to blow your heads off, I'll kill your whole family, I'll spray your house with bullets."

West then picked up a shotgun from his lap and pointed it through the passenger window at his ex-girlfriend's mother, with his finger on the trigger.

Williams immediately pushed West's hand down, causing West to pull the trigger.

The round hit the inside of the front passenger door, leaving a 5cm hole. The two men then sped off.

Police found the smouldering remains of the Rav 4 in bushland at Berkeley just hours after West was arrested two days later.

The gun was found 400m down the same track.

West was arrested two days later. He has since pleaded guilty to four charges including intimidation and firing a gun in a manner likely to injure.

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During a sentencing hearing in Wollongong District Court on Friday, defence barrister Scott Fraser said West had had a traumatic and disadvantaged childhood leading to long-standing drug abuse and mental health issues.

"At 20 years of age he's still relatively young; he's still at a point where studies have shown he's still developing [mentally]," Mr Fraser said.

Judge Andrew Haesler said it was obvious from West's actions that he was "grossly immature" and needed significant help, however noted he continued to resist professional intervention.

"He will have to earn his release," Judge Haesler said, in setting a non-parole period of three years and two months.

"If he continues refusing assistance, if he continues his attitude of defiance, he will serve his entire sentence (in jail)."

The court heard a psychologist assessed West as being at a "moderate to high" risk of reoffending.

"He will need careful monitoring on release...focussing on anger, aggression and his impulsiveness," Judge Haesler said.

Meanwhile, a victim impact statement tendered to the court revealed West's ex-girlfriend was still struggling from the trauma of what unfolded that afternoon.

"I still can't sleep properly....I feel like I'm still living the nightmare," she wrote.

"No counselling will ever get rid of the memories and images I have."

With time served, West will first become eligible to apply for parole in October 2021.