That is a sweet looking half. I'm not real experienced in grading commens but I'll give it a go. Very clean, I'm not seeing any wear on the high points, a couple nicks on Lee's horse's neck, a small rim ding at 11:00, a light golden hue of tinting. Maybe a small scratch just to the right of Liberty on the reverse. I've got to go MS65+ with only the rim ding holding it down. I would love to have this in my collection.
Very nice, clean, lustrous looking coin. I'd imagine this is MS65. Depending on when this was slabbed, I could see this going 65+, but I think it's shy of 66. Regardless of grade, this is a beautiful specimen; most Stone Mountain commemoratives I've seen have rather unattractive toning.
I was thinking about going for 66 but the amount of people that said 64 and closer look changed my mind to 65 to me it's a little over graded.
I'd be interested in hearing what makes you feel it's over graded. I had a choice of two, and this to me looked better. The other was PCGS and had more chatter and some spots that I didn't like. I do think previous guesses do tend to influence future guesses on GTG's.
I thought 65 (before I saw the reveal) because of the reed mark on Traveller's neck and what looks like a vertical mark on the right side of the eagle's breast. Very lustrous coin.