Is a 1887 OCT 4th Patent Harrington Richardson Revolver with the serial 8460 a collectors gun and when was this one manufactured?

It is, most likely with that barrel rib stamping, a 1st Model 2nd Variation "Auto Ejecting" model - made before 1890 - earliest production of this variation was around 1886-87. In Excellent collectible condition, these will bring close to $300 at auction.