Back in the day, when I was casting with brand X and brand Y molds using a bottom pour pot, I often found it helpful to smoke the cavity. The smoke acts as an insulator and helps the molten lead stay molten for a split second longer. I now realize that the root problem was with the bottom pour pots and with the brand X and brand y molds.
10-4. I opened up my bottom pour spout then cast 256 7/8oz 12ga slugs & it "pees like a horse!" Hope to 'get it wet' today, as it's in the high 20's so I can crack the garage doors without getting frostbite, eh.