I recently purchased two Lee 6 banger Moulds. TL452-230-TC, and 358-158-RF. I have not used them yet as I am heat treating (?) them on my hot plate. Sprayed the moulds with brake cleaner (the correct non-oil bc). Soaked and washed them in water as hot as I can stand, used old toothbrush with Palmolive dish soap. Allowed to dry. Heated them to about 220f degrees and allowed to cool to room temperature twice. Cleaned them again with dish soap and toothbrush. Put them back on the hot plate and heated to appx 400F. Will do this twice before I clean them again.
I have never tried to break in a mould in this manner. I just always accepted the fact that I would have to cast a lot of bad boolits before getting good ones. Giving this a try. Maybe it will stress relieve the moulds and help condition them, or not.
Had to remove burrs on the 452 mould and had to lightly stone the 358 sprue plate because it had material that was dragging on the top mould surface. Going to properly lube the moulds before putting them into service. Will post an update when I have results.