Christopher Cunningham, in his mid 30s, fronted the ACT Supreme Court on Tuesday after pleading not guilty to intentionally inflicting grievous bodily harm and unauthorised possession of a gun.

He also entered the same plea to firing a gun to cause fear to a person, a back-up charge to the bodily harm charge.

In his opening statement, Crown prosecutor Marcus Dyason said that in March 2019, Mr Cunningham was at the house of a friend, Alex Dimitrov, who was set to meet the alleged victim, Graham O'Neil, about a debt.

Mr O'Neil had been at a birthday party before he and five others arrived at the Theodore premises.

Upon arrival, the alleged victim started calling out for Mr Dimitrov but was met with a woman telling them words to the effect of "the police are coming".

The group turned around and began to leave when Mr Cunningham allegedly shot once into the air, prompting the group to run, before firing about half a dozen bullets towards them.

One bullet hit Mr O'Neil's right thigh that left him being taken to the Canberra Hospital.

The prosecutor said the trial would hear evidence that prior to the incident, Mr Cunningham and Mr O'Neil had an argument on the phone.

Mr Dyason said after the alleged offending, the accused called an ex-partner, saying "I've done something stupid, I need to come say goodbye [to their child]".

After being asked "why did you do it?" by another woman in November 2019, Mr Cunningham said: "The guy I shot was threatening to blow my head off first".

"Something happened to the gun and it started shooting bullets left, right and centre. I loaded the gun again and shot him in the leg," he allegedly said.

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Mr Dyason said the trial would also hear evidence from the doctor who treated Mr O'Neil and the paramedics with the latter expected to say that "several young men" from the group were "quite panicked".

"It's probably understandable - their friend had just been shot and there was a significant amount of blood coming from his leg," he said.

Following the incident, police executed a search warrant at Mr Cunningham's Calwell house and found a rifle they allege was in his unauthorised possession.

Mr Dyason alleges that the gun found was consistent with the one used in the shooting.

The court heard that during a police interview, Mr Cunningham denied being involved in the incident.

For the grievous bodily harm charge, the Crown also relies on the statutory alternative of recklessly, rather than intentionally, inflicting it.

Defence lawyer Margaret Jones SC did not make an opening statement.

The trial before Justice David Mossop continues.

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