The "high" base-ring and the somewhat-smeared flat-bottomed grooves mean it is a FIRED civil war .58-caliber 3-groove "US Regulation made by Williams" Minie-bullet. Yes, the indention which encircles its nose was made by hard impact by the ramrod during muzzle-loading the bullet. I'd post a photo showing an unfired one, but my computer died this afternoon, and I'm using my wife's Notebook.
By the way... the photo posted by DCMatt shows another version of 3-groove Minie, one whose nose-cone got "engraved" by the pointed twisting arms of a double-helix bulletworm... not by a ramrod.