Might be the weight...4 kilos
Are you sure it is a cannonball?
Sounds more like a put shot, as in track and field shot put. As already pointed out by Chickenfoot, 4K likely stands for "4 Kilograms", which is about the right weight for a put shot. Good luck.
Other people asked questions on similar topics, check out the answers they received:
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them