For.. my own reasons.. I needed a whole lot of 12mm lead balls.
Previously I had cast a bunch of 9mm balls using a modified fishing sinker mold, an old sauspan, the gas hotplate, and my wifes absense....
But now I needed a WHOLE LOT of 12mm balls.
So I lashed up the below, part of which consisted of a commercial, 50 cal ball mold (which I highly recommend).
If you google 'bullet casting' you'll find lots of pics that give the general arrangement of the lead casting pot.
My tips are:
The pot is about 110mm diam by 110mm deep. I used 2x 300W cartridge heaters, inserted through stainless compression fittings welded to the rear of the pot. This gives a 15-20min melt time for about 7Kg of lead.
The Temp-o-matic is just an ebay PID controller and solid state relay that has a GPO and thermocouple plug on the back. I use it for all my seldom used temp controlled devices.
The 'valve' is just a tapered pin in an oriface welded to the bottom of the pot. I lapped it in, but I really doubt that this was necessary. What IS necessary is some means of adjusting the lift on said pin to limit max flow. I used a collar and grub screw arrangement. Fiddly to set, but I haven't had to adjust it. Other setups use a screw as a stop.
At a sitting, I'm making about 100 balls, I guess that's about a Kg lead... Happy with that.