River Rat, there are several ID-possibilities for your your bullet, from the civil war era and the postwar era. Also, there are several calibers it might be ...for example, 36, 38, 40, 42, 44 caliber. So, to give you a specific ID (and time-period) for your bullet, we need super-precise measurements of its diameter, its length, and its weight. We also need to see it with the rest of the dirt cleaned off it, and a photo of its base.
At the moment, without that information, going only by its shape, my guess is that it's a .44 caliber Henry Repeating Rifle bullet, missing its copper cartridge-casing ...or a .36-caliber Hazard, or.36 Sage bullet. If the precise measurments prove it's not any of those possibilities, it is a postwar era cartridge bullet.
