brain balls new to me.
So a shrunken (though not by much if the skull is not removed) calcified head.
Not a lime pit - that's a different process entirely. what we're talking about would be lime stone. there is aplace in yorkshire - mother shiptons well. where you can place objects in very hard (mineral bearing) water. and over time they are coated in deposited limestone.
But a full sized human head, with a stone coating would be too large for a hand sling.
Not to mention much too heavy.
So maybe they removed the skull ?
It all seems a weird way to get sling ammo. Perhaps a brain ball was simply another name for a shaped stone missile ?
If you look round the forum there is afair bit of discussion about slings found as grave goods in ireland and a barrow where a lot of slingstones were found. Someone will know the details - after 7 years I just try and remember that these threads exist rather than any fine detail