It appears to be an unfired civil war era yankee .58 caliber 3-groove Minie bullet. Although yours lacks the usual light-grey/white Lead Oxide patina we typically see on bullets which have been in the ground for 150 years, I've personally dug them out of "wet ground" (swamp, marsh, creek-bank) with very little oxidation on them. Or perhaps you cleaned the oxidation off of yours. That type of bullet is still being made and sold today for use by Blackpowdeer Rifle shooters. But I think yours is a 150-yeaar-old one, because the photos show its top and its base have been flattened by hammering. (Somebody sat it on a hard surface and hammered on its top, which caused the base to be compressed outward and flattened where it touched the hard surface). We know that bored civil war soldiers did such things to bullets. (I've dug lots of hammered-on civil war ones here in Virginia during the past 30-something years.) I think its much less likely that a modernday Blackpowder shooter would hammer on one of his reproduction Minie-bullets. So, yours is more likely to be from the civil war era.
Generally, where you dig one UNFIRED civil war bullet, there are more of them nearby. Keep hunting that spot, and let us know if you find others.