The incident was reported last week after the shot was fired in a weapons room with reinforcement weapons.
It happened in connection with the weapon being emptied of shots before a work shift.
The dangerous shot went through a wall and was close to hitting a craftsman on the other side of the wall, according to the report that the police authority submitted to the Swedish Work Environment Authority.
In addition to the police who had the weapon, there were two other people in the armory.
After the incident, everyone had pain in their ears and had to contact the health service to get information on how to rest their ears.
Neither hearing protection nor the intended cartridge case was used at the time.