Marketed to farmers, riders and others who worked with livestock, the Humane Horse Killer was purposely-built for putting down injured or sick horses. When collapsed, the Horse Killer measures 6 1/2 inches long, and is marked, "GREENER'S HUMANE HORSE KILLER/ W.W. GREENER MAKER LONDON & BIRMINGHAM" on the tube, and the "muzzle" is marked "TOP" on top and "Mk1*/ broad arrow" on the front. Opened up, the pistol measures 10 1/2 inches long, with a screw-off breech and the brass end cap serving (and marked) as the mallet for striking the spring loaded firing pin. In use, the gun is placed against the animal's forehead, with the slant of the muzzle permitting a straight shot through the brain, and the outer tube doubling as an expansion chamber. The number 4 has been painted on the barrel. Matching numbers on barrel and breech, both Birmingham proofed, and matching partial numbers on the outer casing and mallet.

Very fine, with approximately 80% of the original blue finish, showing the start of a mixed gray and brown patina on the exterior and mild handling marks overall. The brass is well aged, with a number of dings and handling marks, particularly a set of 20 dings on the striking face of the mallet. Mechanically excellent.