As the teenage girl tried to wrench the sawn-off shotgun from Ashman's hands, it went off with the shot going through Dwayne Wright's screen door and into his chest.

There's no evidence Ashman knew the gun was loaded or intended to kill Mr Wright at Altona in Melbourne's southwest two days before Christmas in 2018.

Ashman will now spend at least four years in jail for manslaughter.

His 26-year-old victim was on the autism spectrum and called Ashman a pedophile before being shot.

An argument had broken out when Mr Wright yelled for the stepdaughter's dogs to shut up after returning home on December 23.

Jemma Chumbley, 19, said "stop screaming at my dogs" and "I don't want to be scared in my own house" before going to the man's door armed with a baseball bat.

Mr Wright told Ms Chumbley he knew when she was home alone and would have her house run through, before Ashman joined them with a gun.

"Get away from that junkie, he's not worth it," he said.

"I do ice, it's not as bad as weed," Mr Wright replied, as well as calling the stepfather a pedophile.

Ashman pulled out the 12-gauge sawn-off shotgun and it went off as Ms Chumbley tried to grab it. They then left the scene and police found Mr Wright's body behind his screen door.

The gun is still missing.

Ashman was originally charged with murder, but last year pleaded guilty to manslaughter.

The Supreme Court of Victoria's Justice John Champion said Ashman "acted in a cowardly, provocative and aggressive manner towards an unarmed and innocent man".

"Your actions were fuelled with anger, which involved carrying a firearm and were prompted by a completely pointless reason," he said.

"This was, as is so often the case, a lethal combination."

Ashman was jailed for six years, and must serve four before being eligible for release on parole.

He has already spent 437 days in pre-sentence detention.

Australian Associated Press