What kind of bullet killed abrham lilcoln?

According to the National Archives, John Wilkes Booth killed President Lincoln with a shot in the back of the head near his left ear. The pistol he used was manufactured by Henry Derringer, a .44 caliber about 6 inches long with a 2 1/2 inch barrel and only weighs 8 ounces. The weapon was found on the floor of the State Box in Ford's Theatre after the assassination, but it located today in the basement of Ford's Theatre.