Note that this Minie-bullet's nose has a distinctive small flat tip, which is a sign that it was "nose-cast." That term means the bullet-casting mold's filler hole was at the top of the bullet. Therefore, when the cast bullet is removed from the mold, it has a small short projection of lead, called a "casting sprue," on its nose-tip. The sprue was usually snipped off, creating the small flat area on the bullet's nose-tip.
Instead of using the ancient molten-metal casting method for making bullets (which often produced imperfections in the bullets), the US Ordnance Department preferred to have bullets made by using a machine-press to compress a slug of lead (cut from a cylindrical bar of lead) into the desired shape of bullet. Therefore, nearly all nose-cast civil war Minie bullets were made by the Confederates, who -- unlike the massively industrialized north -- possessed only a comparative few bullet-press machines.
In summary... your bullet appears to be a latter-war (1864-65) Confederate-made 3-groove Minie bullet.
