Nice finds. You can find a lot of perfectly round rocks in areas that were near the edge of ancient seas. There is a place along SH-19 in Caddo County, Oklahoma where a bunch of these occur. People would go there and get them and use them as forms for shaping rawhide rattles. People still use them for that, but the rawhide rattle has pretty much become a sort of old school thing. Gourds and Calumet baking powder cans are the more current thing.