Unbelievably, I've found some information about the owner of the gun. Scratched into the butt is: C Smith April 29, 1861. I found three pieces of correspondence between a C Smith and an Overland Stage agent named Nat Stein in the University of Utah's Manuscript Library dated 1865, and the signatures on the letters are a spot-on match to the scratched signature on the gun butt. It's almost a dead certainty that they are one and the same person. From the context of the letters, C Smith was likely a station agent in charge of two or three stations in present day southwest Montana; Red Rock (creek), Horse Prairie Station, and possibly Junction Station, all three of which I've located. In one of the letters, he writes of "returning to the states" soon, which leads me to believe the gun could have been lost on a trip to Fort Benton shortly after the letter was written in 1865. Of course, it's entirely possible Mr. Smith made several trips to and from Fort Benton too, and it could have been lost anytime clear back to sometime in 1861. It's also possible that "returning to the states", he had no further use for the revolver and sold it before leaving too and the next owner lost it. Who knows. Fascinating stuff, this history.
Sometimes the squeaky wheel gets replaced...