On Christmas Day he was at his father-in-law's farm and loaded two bullets into the collector's gun his father owned to try it out.
On forcing the barrel shut, it went off, shooting him in the hand, narrowly missing two knuckles but breaking a finger in his left hand.
Police took his gun licence a month later when he was charged and he hasn't shot a gun since.
Defence lawyer Jock Blathwayt said a conviction would have a serious impact on his client's ability to take part in shooting competitions.
Judge Morris said a conviction of unlawful possession of a pistol would raise too many questions by authorities when Mr Mende travelled overseas to compete competitively, impacting seriously on his sport because the offence "suggests something more sinister".
"Any possession of a pistol unlawfully is serious."
Police had taken a "sensible, compassionate approach" to the charges, Judge Morris said.
Outside court, Mr Mende said he was pleased it was all behind him.
"I just want to shoot again," he said. "It leaves the way open to get my licence back."
Mr Mende is a champion speed steel and cowboy action shooter and said such a conviction would have disqualified him from competing and travelling overseas to compete.
He and his dad, Doug, are keen shooters who say they "don't hunt, we are target shooters. It's a sport."
Mr Mende snr has six gold medals notched on his holster. The pair are hoping to go to the World Cowboy Action Championship next year.
"As a team, we are up there," he said.