When I made lead media I used wooden molds. Drill large holes on a piece of wood clamped to a wood backing plate so holes will be cleaner. Remove the backing plate and clamp the wood with holes tightly to another (flat)piece of wood.Pour in the melted lead, let it cool and knock them out with a hammer and punch.If you drill the holes close to the edge they will come out easier as the wood will break.
Yes, that's the way to do it, I follow the exact same procedure when casting lead milling media.