Sorry to have to say, it absolutely is not a civil war bullet. In particular, it is not bullet #47 nor #48 at the Army Of Tennessee Relics website, because T-Net member therelichunter's bullet has a VERY-slightly raised flat band -- or a crimp-mark -- around the bullet just above the deep body-groove. It is a modern bullet, made for re-loading spent cartridge casings. See photo below, showing one which was crimped into a casing, and has been fired.
That modern-made .45 lead bullet for casing re-loading is shown at the following link as bullet #452374, except the one there does not have the crimp-mark, because it hasn't yet been crimped into a casing.