Terry
The problem you have is that you live in an area where the shoreline has been re done by moher Nature and Hurricanes many times since the 1860's. Perhaps you could talk to the people out on Cat Island at the Civil War era fort there and get some historical information. That Shoreline has ben pushed back and forth many times over the intervening years and the sandy soils are very porous for objects to sink into.
I would seek out Historical Societies in the area and see if archives exist. As you know the entire regions been wiped out a few times and likely records have ben lost destroyed. Seek for older cemetary locations as the dead in those days were often buried near where they fell.
Good luck..
