One of three (3) cartridge packs for Army Pistol (Colt).
C - Wood block wrapped in paper, printed, "6 Combustible Envelope / CARTRIDGES / Made of American Powder Co.'s Powder; / For Remington's, Colt's, and other / Navy or Bell Pistols / …100 Inch Calibre. / …TED SUPERIOR QUALITY".
One box (a) of cartridges came from the last rounds of cartridges issued to Mosby's men in 1864.
The history on the other two boxes of cartridges (b, c) may or may not share this provenance.