Re: I bet you won't get this one... I don't even know where to start! (NEW PICS!)
Clearly the two halves were made in a mold(s) and then put together. The clay used to stick the two pieces together is easily seen and crudely finished. From this information you can deduce that it was made that way because they could not make it in one piece or they wanted to put something inside it. If it is truly ceramic and there is something in it then whatever is inside it would have to be able to withstand the heat of firing the ball. To find out if there is something in it you could have it xrayed, cut it open, or weigh it and then weigh it using the method to find out if the specific gravity is different(method used to weigh nugget specimens in quartz). The inside could be lead, maybe even gold, maybe somebody was smuggling gold hidden in it, not likely though. If you do decide to open it be very carefull. A tile saw would cut that in about 15 seconds.
Due to the crude fabrication I still say it is a projectile. Probably used for a sling. The perfect sling projectile is about that size and round. You could literally make hundreds of those in a day or two and not worry about losing them. Much easier than trying to make a rock perfectly(or close) round.
http://en.wikipedia.org/wiki/Sling_(weapon)#Ammunition
