Good Afternoon Squirrel Pizza,
This thread is a bit old, but I will post some observations anyway.
First, you have established that the swagged ball shoots accurately. Therefore, the problem must be the cast ball.
I have cast thousands of balls over the years, but that DOES NOT make me an expert on the subject, but let's give this aGO ANYWAY.
If the ball exterior is smooth with no surface defects, the first step has been passed. Next, did you weigh the balls? That is a MUST step. A plus/minus .2 (two tenths) of a grain is my standard tolerance. Less is even better. I ALWAYS wear medical type rubber gloves when weighing balls. You should also.
Keep all that are heaver for practice. Throw all lighter balls back into the melting pot. Those that are a consistent .3 lighter can be kept for 25 yard practice but no more. Cut some of your reject lighter balls in half with a sharp knife. Pure lead is so soft, it is not hard to cut a ball in half. The lighter balls will most usually have a void in the center.
Try the weighing and report back with your findings. Let us hope that weighing and sorting will solve the problem. If not, then Plan B.
My respects to All,
John L. Hinnant
:God and Texas"