Original Remington-Keene carbine made circa 1880 for the commercial market. Chambered in .45-70.
The design was Remington’s entry for the 1879 US Army repeating rifle trials. It has some strange features including the false hammer on the back of the bolt and the bottom loading gate, which seems to be the first appearance of that system since pump shotguns didn’t exist yet. It lost out to the Winchester-Hotchkiss and the Remington-Lee, although the Army ultimately decided not to adopt any of them. The US Navy did buy a few hundred, though.