Cannonball? Shotput? Something else entirely?

[Ammez]

Hello! Can anyone help me identify what I have here? Found it in a weird "free" store in Oakland, CA. It is spherical but uneven, almost like it was hand formed but feels like metal. It rattles a bit with things that sound like ball bearings inside. There are no letters or markings on the outside and it measures about 3 inches.

 

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[TheCannonballGuy]

I don't know what it is, but I can assure you that it definitely is neither a cannonball nor a Shot Put ball. Those kinds of balls are always perfectly spherical... never out-of-round like your "Free Store" find.

 

[Gambrinus]

Because it is out of round, my guess is that it could be a used "ball mill" ball. But it being hollow doesn't fit that guess unless there was an unintentional void in the casting.
I know if I had it, I would cut it in half just out of curiosity. But that is not a suggestion.