Ethan Maurice McPherson pleaded guilty in April 2023 to unlawful striking leading to the death of David Murphy at Springfield Lakes, southwest of Brisbane.

He was sentenced to eight-and-a-half years' imprisonment with a requirement to serve 80 per cent of the term before being eligible for parole.

McPherson last week represented himself before the Court of Appeal in Brisbane and argued his claimed efforts to avoid a fight had been "elevated to premeditation" and delivered him a "very severe" prison term.

Justices Debra Mullins, Hugh Fraser and Declan Kelly on Tuesday refused McPherson leave to appeal.

"McPherson has failed to show that, in all the circumstances applying to him and his offending, the sentence imposed for the unlawful striking was 'unreasonable or plainly unjust'," they stated in their decision.

The justices said McPherson's sentence was already shorter than his offending would require as he suffered a brain injury after being stabbed and stomped on by three men while on remand.

McPherson previously told the court he made a verbal threat to Mr Murphy in an attempt to avoid violence.

"I knew something was going to happen. I said 'I'm going to shoot you'. I tried to scare him off," McPherson said.

Mr Murphy had been celebrating his 49th birthday with family members on the evening of October 19, 2019, when his group and McPherson's group had a confrontation beside a road.

A man travelling in the same car as Mr Murphy punched one of McPherson's friends.

In return McPherson, then aged 19, pulled out a shortened, bolt-action rifle and threatened to shoot.

Mr Murphy put his arms out and said, "Go on, shoot me" before McPherson instead used the rifle butt to hit him in the face, causing him to hit his head on a gutter.

Mr Murphy was declared dead at the scene by paramedics.

McPherson will be able to apply for parole in 2026 due to time served on remand.

Australian Associated Press