I'm probably the last person to answer a question like this. I'm new to metal detecting and certainly no expert in civil war relics. I did a little googling and found most of the square CSA buckles claimed to be authentic all have three prongs on the back, yours seems to have four. Also the CSA stamp goes all the way through the buckle. The ones I looked at the stamp doesn't appear on the back side. Does that mean it isn't authentic, I dunno. I'd be thrilled to pull it out of the ground either way...