Your find is a scarce Confederate variant of .52 "Ringtail" Sharps bullet. Believed to be CS because we dig this particular version mostly in CS Cavalry encampment sites. It is nicknamed the "Christmas Tree Ringtail Sharps" because its profile (viewed from the side) matches up pretty well with the profile of a Christmas tree. Pointed top, taper gets wider as you descend, upper body-ring is smallest, middle body-ring is a bit larger, bottom body-ring is much bigger (in diameter) than the other rings, and the "tree" is sitting in a wide water-basin.
By the way... thank you VERY much for the closeup photos which show the bullet in a digital Caliper's jaws, telling us its very-precise size measurements. I wish more people asking for bullet ID would do that.