I found it strange too, I have worked with metal for 25 plus years and have not had that happen before. Heck maybe it has something to do with the elevation (7035 ft) I live at?

I have another question, I have heard of guy's making their bullets buy cooling the mold in water? did I hear that right? I thought if the mold was to cold the lead wouldn't flow into all the little grooves in it.