J. M. Carpenter had joined Co. "H", 12th Mississippi Cavalry Battalion (later 10th Mississippi Cavalry), but was elected Captain of Co. "A", Ashcraft's Mississippi Cavalry. His military service record with Ashcraft's Cavalry includes a postcard dated Mar. 3, 1931 from Ira Smith, Marianna AK. Mr. Smith paid two cents postage to write the U.S. War Department about Captain Carpenter's military service file, which includes signed receipts, rolls &c. It also includes a notice of election to fill the vacancy created by Carpenter's death on July 28, 1864.
It costs more today, but copies of both the service files you mentioned are available here --