Interesting. I agree that plummet looks odd, I've never seen that style with such a pointy end. But Poverty Point people made a lot of cool plummets, so maybe
I've long since forgotten who has the frame, but there was a frame of Cahokia points collected by a guy who either worked at a turkey processing plant or raised turkeys. They were on a Cahokian site and turkeys would scratch up and swallow gizzard stones, which left them polished.
This is the frame, but similar points on Pete Bostrom's site.Gizzard Stone Cahokia Points