Army private was going to swap uniform for plumber's overalls.
Private Michael Ross was weeks away from being discharged from the army when his rifle apparently knocked him unconscious as he fell from an inflatable boat.
Private Ross disappeared under the water and his body was found a week later.
The family of the soldier believe he was unable to inflate his lifejacket after falling into Lake Moawhango, near Waiouru, because he was unconscious after being hit by the butt of his gun in a freak accident.
Private Ross, 29, had handed in his notice to the military only weeks before he drowned in the lake during an army exercise on September 25.