That civil war .69-caliber Minie-bullet is listed in the bullet books as a Tower, because it was made for use in the .69 Tower-Enfield rifle-musket. Yours appears to be the British-made version, which has a flat-bottomed "plug" cavity instead of a cone cavity. It's a fairly scarce bullet. Most that have been dug come from the Confederate entrenchments at the Port Hudson LA battlefield... which "fits" with you being a Louisiana digger.