Hmm. Those are interesting. My initial thought was that they might be one of the many cannonball look-alikes (shot puts, counter weights, etc), but then I wasn't so sure. Could these be coehorn shells filled with metal? I've seen this before. I once had a Confederate shell filled completely with lead. The protruding bronze could be sprue? Or were they bar or chain shot, but cut down over time? Or are they just the top of a flagpole?
Hopefully those more knowledgeable on ordnance will chime in-