An outstanding book on the subject is "Archaeology, History, and Custer's Last Battle" by Richard Allan Fox, Jr. By using bullet/cartridge "fingerprinting" on cartridge casings and bullets gathered up from around the battlefield, the archaeological team was able to follow individual weapons (and, as a result, those firing them) around the battlefield to different locations. Some fascinating detective work, as well as a number of different theories as to the flow of the battle. 