It is DEFINITELY a modernday "Lyman-Mold" imitation of a civil war 3-groove minie, made for use by Blackpowder Rifle shooters. The key ID-clues are the unusually short "nose" above very-wide-spaced (and deep) grooves, in combination with a very-deep base cavity with very thin "skirt" (rim around the base cavity). Go to the following website, which sells Lyman-Mold and Ideal bullets, and scroll (a long way) down to bullet #575213.
I should mention, I've got a jar full of those, in still-shiny condition, here at my house. I also dug a bunch of fired ones near the Cold Harbor VA battlefield. I'll never forget that very frustrating afternoon of swinging the detector (and shovel) in the woods.