If you can only find one coin during a 2 hour hunt, it might as well be a reale. Sadly, my specimen is very worn. No date visible, but I believe its a Carlos III half reale.
That Half Real is a nice find, smooth or not. I've only found one, and it isn't much better than yours, but since I live in Illinois and they don't pop up here very often, finding that coin was just as good as finding a gold coin (to me).