There were some 1850s patterns that had the eagle facing right, but with the stippled background I *think* what you have there might be a post-CW plate. Not post-war by much though.
It is the US Model-1874 "Eagle-Wreath" buckle. Your specific version, showing the eagle looking toward the right side of the buckle, made by Horstmann of Philadelphia, was maufactured from 1874 to 1890. See plate #915 on page 543 of the book "American Military Belt Plates."