Mohammad Jahan, a constable of the combat battalion of Calcutta police, allegedly misfired his 9mm pistol while loading it, hitting colleague Chanchal Sardar at the police training school on Friday morning.
An inquiry revealed that the pistolís safety catch was open when Jahan was trying to load it.
A safety catch is a small lever below the gunís barrel that can lock its movement, said a weapons expert.
ďSardar, who was a few feet away, suffered a bleeding injury after the bullet grazed his finger. He has been admitted to hospital. A detailed report has been sought from the deputy commissioner, combat battalion,Ē said a police officer.