It's a bullet mold for old lead bullets.

I just got back from china. The thousand year old eggs are certainly a curiosity. They form little snowflake-like crystals on the backs of them. They're really pretty looking, like amber or something. The taste is... unusual, but not unpleasant. Trust me there are MUCH stranger foods in China. Smelly Tofu, for instance, can be smelt miles away. Not a pleasant food for foreigners.