Revolver found in Grace Dunbar's wardrobe

“A revolver with one discharged chamber and a calibre which corresponded with the bullet was found on the floor of her wardrobe.” (Sherlock Holmes)
“It was his pistol, you know.”
“Was that clearly made out?”
“Yes, sir. It was one of a pair that he had.”
“One of a pair? Where is the other?”
“Well, the gentleman has a lot of firearms of one sort and another. We never quite matched that particular pistol — but the box was made for two.” (Sergeant Coventry)