Sorry to have to tell you, the item is not an artillery projectile nor any part of one.
Back in the late-1970s, my co-author on the civil war artillery projectiles book, Tom Dickey, had a literal pile of that item in his backyard, because people kept bringing them to him thinking they were a civil war artillery item (and then abandoning them when given the bad news). Tom felt they were some kind of machinery-part. Despite doing a good deal of research on them since then, I have been unable to discover "specifically" what they were used for. But I am quite certain they are not an Artillery item. For one thing, their very short cylindrical body is much too short to perform properly as a Rifled Artillery projectile. For another, keep in mind that they are solid (not hollow for containing an explosive charge). Also, keep in mind that, if they were an artillery projectile, like, let's say, a Solid-Shot cannonball, every one of them would be a "dud." Since they do not explode, if they are an artillery projectile, a good number should get found on battlefields (such as, impacted into the outer face of a cannon-emplacement or other fortification). But of the hundreds which have been found, very nearly none have been dug on a battlefield. In actual fact, they most frequently are found on Ebay ...in "non-excavated" condition.
Regards,
Pete [P.C. George]