I would also say that the melt and the mold are not hot enough.
Jerry, FWIW; I have found over the years that running the melt and the mold real HOT is a definite plus, maintaining that proper heat is a matter of cadence, or timing, that's easily learned through repetition....your temperature, your mold, and your alloy will set that pace for you, you just have to determine how fast, how slow, that pace is when things look their very best
Always make a small puddle on the pour hole with your lead, when it's time to cut the sprue, using the sprue plate, a small dimple or indent will appear on the top of that pour, that tells you the air bubble/bubbles are gone from the ball, making your throws more consistent in weight
I have also discovered that dropping a hot ball on a heavy, damp, soft towel will keep the ball true.
When I'm running a lot of ball, say 100 plus, I will change out the towel with a fresh one about half way through, at that time you can actually pick up the ball with your fingers.
Uncle Russ...