The guess made by Ffuries (he said "might be") about your bullet is correct. It is from the 2nd half of the 20th Century, and is still being made today. Specifically, it is named a MaxiBall, made for use in Blackpowder rifles. See the photos below. There is more than one caliber of Maxi Ball, and three body-versions. As seen in one of the photos, some of the MaxiBalls we dig have been in the ground long enough to develop the typical grey-white lead oxide patina we see on excavated civil war bullets.