I quote from Flayderman (p.314, 9th Edition):

"Major variations were:
RIFLE; The Flatside Model, the frame sides without escalloping or fluting; standard barrel lengths vary according to caliber, and are usually round;..."

That implies that octagon barrels are to be encountered, at least in Flatsides (S/N range 1-5000), and while not mentioned, probably (or possibly) in others as well.

I don't think I've ever seen one, either, but that surely doen't mean here were none as I haven't seen that many 1895s.