Get the mold hot, that it takes 5 to 10 seconds for the sprue to solidify. This is the correct casting temperature range window.
Perfect fill out easy bullets dropping and slight frosting happens here.
Somewhere in this temperature range window you're going to find what works for you.
Now get it hotter, a very slight overheat. Should take about 15 seconds for the sprue plate to solidify. This is the cleaning temperature.
Get yourself a new clean white cotton rag and cut it into quarters. Use one of those rag pieces and dab it a bit with some synthetic two cycle oil, and wipe down everything, scrub all surfaces of the mold with the oilled rag.
This is the easiest and least time wasting way and least damaging way to clean the mold. The lead smears on the blocks will come right off. All the surfaces will now have a very very thin film of oil. Get back to your regular casting after doing this.
After three or four casts any oil that was in the cavities will have burned off.
Heat management is absolutely critical for the brass mold to function well.
Be safe.
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