Dave, I recently read parts of Last Chance for Victory By Scott Bowden, Bill Ward at http://books.google.com/books?id=EHZ9dD_5k7UC&pg=PA312&lpg=PA312&dq=21st+mississippi&source=bl&ots=rcVY_GFTFG&sig=SMrslPBz3tpNtp_g7STvUBu4UCo&hl=en&sa=X&oi=book_result&resnum=8&ct=result#PPA318,M1
that writes of some of the 21st movements at Gettysburg.
r/Steven