Antique Cane Air Gun

Pricing & History
metal cane air gun. Appears to be a single shot cane air rifle. All metal except the horn end cap that screws on. Paint is chipping. Measures 36 inches long. Untested and unsure if it is complete or functional. Handle cap unscrews to reveal some numbers, 15591 5 ? Unscrews in the middle, to reveal a firing mechanism. Lower half contains a rifled brass barrel that unscrews from the end and slides out. 2 small iron sights. It also has 2 holes, one doesn't move, but the other seems to have an adjustment location or something, see photos. I cannot locate any further manufacturers or proof marks. No air pump or any other accessories.