Sgt Collin said the man holds a current New Zealand firearms licence and the gun was stored in a safe.
The court heard the man loaded the weapon with shells and believed he had then completely unloaded it. But as he began to dismantle it, it fired.
"He stated he must have had his finger on the trigger.''
Sgt Collin said unbeknown to the man, his wife had entered the garage through the access door and come around their car.
She was shot. The distance away she was or the number of pellets which hit her were not mentioned in court.
The man helped his wife and called an ambulance. He spoke to police and then went to be with her in hospital.
"He was extremely remorseful and shocked.''
The man pleaded guilty to the charge but a conviction was not entered. Lawyer Louise Denton said she intended to apply for a discharge without conviction.
The man's name and occupation have been suppressed on the grounds he would experience undue hardship were the details made public.
The discharge without conviction application was due to be heard on June 12. The man has been remanded at large.