I volunteer as a docent with the Sacramento Museum .... I thought I was pretty knowledgeable about the history of firearms, but I had never heard or read of such a firearm until I saw one in a museum case ... the stock on this one dropped down like an old East Coast flintlock, so I am guessing the time period of this to be around that period.
If I am ever allowed access to it, I will get pictures and caliber of the weapon ... and maker, year of manufacture, etc.
BTW, it shoots five rounds at each loading, and I am guessing it to be a .36 Cal.