"air bubbles" in the cast bullet alloy will throw the weights around bullet to bullet. I suspect.
what i haven't done yet but keep threatening to do is make a duplex lead bullet. Soft nose followed by a hard shank.
not like it hasn't been done before.
I have at least a half dozen of these combinations i need to run into water jugs/chrony. But then it's only in the 90's now, as usual i probably will wait till it's 115 in the shade on the desert.
lyman mentions it in some of their faq's. more noticable on big bullets and when the mold in not venting properly.
https://www.lymanproducts.com/lyman/faqs/bullet-casting.php
