I wish I knew for sure that your/our brass bore-cleaning brush was from the civil war, or from later. As I indicated above a significant quantity have been dug at civil war sites, so we always assumed they were from that time-period. But despite much online searching, I have not yet found any documentation that "our" long-with-threaded-end version of the bore brush was manufactured before 1866.
What is the total length of the one you found? As you see in the previously posted photos, most seem to be a good bit shorter than yours.