I bought a Lee six-cavity 158 grain SWC tumble lube mold, went through the normal preparation ritual (cleaned it, alcohol, candle smoke, etc...) but about 1/3 of my bullets seem to have a "dent" in the middle of them. The tumble lube groove is still molded in, but it looks like it's collapsed on the side. Is this normal? I cast 230gr LRN tumble lube bullets and don't have this problem from them. Any idea what I am doing wrong?