Yep! You got yourself a Civil War minnie ball. This type is called a Williams Cleaner Type 2. They were issued to the soldiers, maybe one of these in every pack of bullets. The purpose of this type of bullet was to clean the inside of the barrel when it was shot. The insert on the bottom would expand and run along the inside of the barrel. You will find them in unused, "dropped" condition like this more often than used, "fired". They were believed to be less accurate than regular bullets, so the soldiers just tossed them out. There are a few different types of cleaner bullets. I've found type 1 and type 3, but never type 2. Nice find. Congrads. Is this your first Civil War find? -Wolf