Basicly the hotter the mold the bigger the ball, the lead tempture when it is to hot will cause a real thin flange around the ball.
For best effect I used to hold the corner of the mold [just a corner and away from where the blocks join] in the melted lead to preheat the mold. After you flux and skim watch the color on the top of the lead you can see a slight color change at different temptures. Don't pour to fast once you get every thing right try and keep the tempture tha same. Its like loading you need every thing the same for best results. Lee