Hi Jef and others.
If you want to make double-conical sling shot bullets out of clay you'll need to dry them in the sun.
And that just might work with the weather we're having now.
Otherwise in NL and B, not a chance.
That's because you'll need the water content for the weight and density.
That's how the old bullets were done anyway.
Baking them makes a bullet dry and brittle.
What also works, and that's one I tried.
Put a pebble (for weight) in some self hardening clay and let it dry slowly.
Not too fast; the clay shrinks and will break if you dry them out too fast.
But please do not use them around anything living or anything you don't want damaged.
Remember a slingshot bullet is capable of killing.
You wouldn't fire a gun or throw a sharp spear either.
What would be an option as well, and makes a much better story, is make a lead bullet mould.
The ones that have been found usually make eleven at once.
In my humble opinion that must be one of first examples of mass production.
If you don't have a picture of one of those moulds I can scan it for you.
(I hope)
Cheers,
Wim/Cordvs