As the bullet's finder noted, its weight of 1.45 oz./634 grains is too much for a .58 minie-bullet. Speaking as an oldtimer Port Hudson digger, the very rounded shape of the bullet's nose strongly suggests it is a .69 Tower Enfield minie... and what looks like a bit of carving on one side suggests that is how it lost some of a .69 Tower's original weight (758 grains). Adding to that ID theory... Port Hudson LA is the number-one source of excavated civil war .69 Tower Enfield minies.
Sidenote:
A .69 French triangle-base minie also has the very-rounded nose, and is very commonly found at Port Hudson -- but the .69 French's weight (516 grains for large triangle, and 581 grains for small triangle) is a good bit less than your bullet's weight.
