What lets you date it to 1880? Are you interpreting a patent stamp to mean it could be no earlier? A serial number in the 400000 range should put its manufacture much later than that, regardless of which serial number range it belongs to.
Condition is everything in valuing older guns, so it would really help if you could post a photo. If that's not possible, a complete description of all stampings on the gun and where they are found would help. Also, does it have an external hammer that can be manually cocked? And is it a top break model in which the barrel and cylinder swing down to eject and reload? Or is it a swing-out model in which the barrel is fixed to the frame, and the cylinder swings to the side to eject and load?
We can answer your questions, but just need a little more info to start with.