Police later charged him with careless use of a firearm causing bodily injury.
Counsel Louise Denton said the gravity of offending was low, because the defendant had believed he was handling the gun carefully.
But prosecuting Sergeant Grant Gerken said the defendant had breached three of the seven golden rules of firearm safety: treating every firearm as loaded, always pointing a firearm in a safe direction, and only loading a firearm when ready to fire it.
By his own admission, the defendant had been tired after not being able to sleep after working a night shift, and had been wrong to think he was in a fit state to be handling firearms, Gerken said.
Judge Farnan said the man's wife did not want him to be convicted, and supported him "unconditionally and absolutely".
She partly blamed herself, and cried every week because of the emotional harm it had caused them both.
The defendant felt "profound remorse and guilt", suffered post-traumatic stress and had been diagnosed with depression.
She accepted a conviction would affect the couple's ability to travel overseas together, which they did often.
She ordered the defendant to donate $1000 to St John Queenstown, and to pay $130 court costs.