So I'm low on 40SW reloads so start casting some last night, I'm using a Lee bottom pour pot with a PID set at 750, using COWW. Everything is going along fine, I've done about 500 or so and topped the pot off a couple times. I top the pot off when it's about 1/3 to 1/2 empty, wait for the temp to reestablish and start back casting. I immediately start getting the below, "finning" at the bottom, like the sprune plate is warped all of a sudden. What causes this and how do I fix it? I've cast thousands and thousands with this particular Lee .401 and never had a problem. Appreciate any help or insights.....did some searches but my google-fu is failing me. Thanks!