Well, first they are BIG as far as a lead slug goes, at least the musket rounds anyway. The pistol rounds are about the size of a modern bullet, but again, can look quite different than today's slugs. They usually have a whitish patina from years in the ground, but not always. You won't see rifling marks on the bullets. Sometimes you will find a 'nipple' at the top of the bullet which is where the ramrod deformed the bullet being pushed down into the barrel. Do a search on "civil war bullet" on google and you will find a load of pictures to look at. There are even some shotgun slugs used during the CW, but I have never found one, again they look different than a modern shotgun slug.