I have a limited amount of information on both William James Nelson Hammett, who was killed in the war, and his son, James Harvey Hammett, who, I understand, attended college postwar (I don't know where), became a doctor, and moved to Yazoo City. Rather than put this on the Message Board, the material not being completely related to the Mississippi Civil War experience, E-Mail me directly at Sturkey@wctel.net, and I will send you what I have, including sources.
I do know that this branch of the Hammett family originally came from Laurens District, S.C.; there was at least one other set -- and I believe several- who came from Spartanburg District. Also, Benjamin Hammett Teague, who was also a member of the Hampton Legion, and later was a founder of the S.C. Dental Association, was also related to the Laurens branch of Hammetts.
I'm trying to find out where James Harvey Hammett is buried, and if the man who died in Yazoo City was in fact the veteran from S.C. His wife, I understand, was Frances Matthews,; they married in 1873.