Last summer Midway had several sales on Lyman, RCBS, and Saeco molds. A few that I picked up had some obvious burrs around the cavities. I casted before I did anything just to see what would happen, and the boolits rolled out with ease. Now the smalled burrs on aluminum and brass molds I purchased from NOE made boolits stick so aggressively that the mold would cool off before I finished rapping at the handle hinge. I could not stop myself from stoning the burrs off the iron molds, and all is well.
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Anyways, seems that iron molds drop boolits more easily than brass or aluminum when a burr is present.