My knowledge of Civil War small arms is limited, and in this area is pretty much non-existent. The weapons in question were in use by the First Texas Sharpshooters in February 1863. The unit had come down to Alexandria via Paris and Jefferson, Texas. One record indicates that one company "received arms" at Alexandria on 15Feb63, so it's possible the guns were from a stockpile of some sort that was in Alexandria. Would this lead you to favor one type over the other?

It would seem strange to arm sharpshooters with smoothbore buck and ball guns, but I'm not sure how significant the "Sharpshooter" designation was.