Thats exactly what mine looked like. My problem wasn't having a mold that was too cold (I was about 600 rounds deep and churning them out), the problem was that when I poured, the sprue wasn't closed all the way (insert Homer Simpson "DOH") and when I tried to open it (even while supplementing the leverage with a screwdriver), it snapped. Fortunately I still have that 45 200 gr. LSWC to keep me busy...
Rev 5:13 "To him who sits on the throne and the Lamb be praise honor and glory and power, for ever and ever"