Australian Olympic shooting champion Michael Diamond has been found guilty of firearms and drink-driving offences, which will see him banned from holding a gun licence for 10 years.

The professional shooter was arrested in May last year in the New South Wales town of Port Stephens.

It had been alleged the 44-year-old was involved in a domestic incident with his brother at Nelson Bay, north of Newcastle, before he was stopped by officers on the road.

Police said he refused to undergo a roadside breath test and when police searched his car they allegedly found a shotgun and 150 rounds of ammunition.

He was charged with high-range drink-driving, not keeping a firearm safe and using a firearm while under the influence of alcohol.

On Thursday, at Raymond Terrace Local Court, Magistrate Caleb Franklin handed Diamond a conviction for the offences and told him the handling of a firearm while intoxicated carried a maximum of five years' imprisonment.

He issued a good behaviour bond for 12 months, but he warned Diamond that if he reoffends he may go to jail.

Magistrate Caleb Franklin said he could not regard the offences as trivial in nature and there needed to be some component of deterrence.

Because of his conviction, Diamond received a mandatory 10-year ban on firearms which will stop him from owning and using a gun over that timeframe.

Diamond was ruled ineligible for nomination for the Rio 2016 Olympics when he was first charged with the offences.

The trap-shooting veteran has competed in six previous Olympic Games.