I'm in the Buffalo Bill camp, but I'll leave the gun identification to the folks here who are smarter than I am.
Many early photographic processes, i.e.: the tintype, ambrotype and the Daugerotype produced images that were reversed left to right. If you wanted an image that would be "correct" you either used a prism or mirror in front of the camera or you took a picture of the picture which would appear correct. The top image appears to be the original image, it being reversed. The bottom image displays a correct rendition, but is of lesser quality, so it is probably a picture of a picture.
Now, it COULD have been done with a glass plate negative... and quite possibly this one was. Much more expensive, but you got better image quality as far as sharpness was concerned and you could make many images from the original negative. These were in use from the early 1850's generally until the 1880's. This isn't a Daugerotype, from the color tone, and while I have seen tintypes colored like this, it looks more like a glass plate negative printed on albumen paper. Why someone would have produced a reversed copy is a mystery to me. The provenance of the original image might provide a clue.
I've encountered glass plate negatives occasionally over the years. You can still make contact prints from them using conventional or POP (Printing Out Paper) if you can find it, but you have to be very careful as the glass and the emulsion on the glass are both very fragile.
I love looking at these period images. Keep 'em coming. In our new digital photography age, images like this are going to be rare because nobody is making photo albums with them... they are just stored online, and when somebody croaks, the imagery mostly gets deleted. I still have and use film cameras, but mostly I shoot digital images these days. Just so much less expensive...
Below is the original image digitally reversed if anyone is interested in a right-reading image of better quality. They didn't have the GIMP back in those days:
