Was just looking at images on google, of cannon ball sabot, and male/female lead connection seals... im pretty sure its a canno ball sabot, we live down the street from a civil war hospital, that supposedely sherman marched through, so dont think it would be uncommon..
Since my name got mentioned... and I came across it... although I can see why some people think the object is part of an artillery projectile, I am 100% certain that the object is not artillery-related, from any era of artillery's history. I think DCMatt's and Fyrfytyr1's guesses are on the right track.
Thank you, BigCypressHunter. It's also good to see you've returned to posting in the What Is It forum. In my view, your knowledge is a big help here. I got your PM last month and sent you a reply. Did you receive it?