What is going on here. This is the second time I've used this mold (lyman 457125). The first time the bullets came out very nice but I was using COWW. Today I'm using a mixture of 3 parts lead and 1 part mono. The dropped bullet just forward of the driving band is leaving a flat spot on the side. Measuring .432 and spinning the bullet in the caliper going up to .451-.452. I tried adjusting the temp, I stored the mold properly and cleaned it two different times when I noticed the slump in the side of the bullet. Seems like it's doing it in the same spot but I can't feel anything on the mold like I can on the bullet. I'm trying to achieve a 13-14 BHN. Do I need to add something to the mix to fill out the mold better or what? I'm open to suggestions. Thanks in advance.
~SP