The Adventure of the Empty House
Holmes and Watson often carry pistols with them to confront criminals—in Watson's case, his old service weapon (probably a Mark III Adams revolver, issued to British troops during the 1870s). Holmes and Watson shoot the eponymous hound in "The Hound of the Baskervilles", and in "The Adventure of the Empty House" Watson pistol-whips Colonel Sebastian Moran. In "The Problem of Thor Bridge", Holmes uses Watson's revolver to solve the case through an experiment.