Do not completely "submerge" your mold when preheating. Just the corner of the mold is all that needs to be submerged. I also don't dip it up to where the mold halves meet. If you do this you run the risk of getting mold in between the blocks and will have to be cleaned out (resulting in finned bullets). ALSO....make sure your mold is ABSOLUTELY CLEAN! ALL the oils from cutting the mold MUST be removed. I use carb/brake cleaner FOLLOWED by a good scrubbing with dish soap and a toothbrush.
~NRA LIFE MEMBER~
~NRA CERTIFIED INSTRUCTOR~