Introduced in 1899, with no caliber markings it is considered a black powder frame. There isn't any serial number chart for the H&Rs until post war. There is a book in the works by Bill Goforth, but with his death it may not get published, The Model is simply " Hammerless H&R ". Basically a American double action with the hammer concealed. Not a Bicycle Gun, that name is taken by Iver Johnson.