Not a bad idea Karl - I used lead stripped from cables to make sinkers as a kid. You could probably make a mold in the dirt with a piece of copper tubing the correct size in the centre to save having to drill out a hole, or punch a copper tube through a tin and have that sitting on dirt before pouring. What to do with the acid though?
As it is I've made this up - not pretty but it works and my 8yo had fun using the power tools to make it
.