I cast with Lyman & Lee molds & have good results mostly .
I store my molds in a airtite container with desicant just as I finished with em .
But every mold I borrow or use for the first time I have fill out or base problems from oils or some kind of residues left behind from cleaners.
I don`t look for "perfect boolits until the 3rd heat cycle (either casting or hot plate) of the mold to get all the hydracarbons out of the pours of the metal.
I`ve read the OP twice & saw no proceedures of cleaning or preheating the mold.
Cleaning & prepping the mold saves me a lot of recycling lead & usually better boolits faster.
Venting is easily over looked , pace of pour ,speed of alloy , temp of alloy & many more things play a part in achieving good results .
My official WAG is ya were looking at each boolit ,thus letting the mold kool off , as it sounds it barely got to temp.
Steel molds were a BIG change for me also, more time for the steel to heat up mostly ,but cured that with a hotplate, just gotta remember to plug it in !!!
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