That's prolly one of the mannicher forends that H&R offered on a special edition 45-70 at one time, the straight stock would be the clue that makes me think that. Also, several years ago Gardner found a bunch of the forends in the storage and offered them to us for $35 shipped IIRC, I put one on one of my 45-70s, they came with a plastic barrel band, but I chose not to use it due to the pressure it puts on the barrel, it shot great without it, never tried it with it.
Tim