I've been doing partial boils in a 5G ss stock pot. Then into the kitchen sink for an ice water bath. I've gotten it down to 67F in 30-45 minutes. But I then started thinking about how the old ice cream makers worked. An aluminum pot was placed in the center,surrounded by ice with salt on it. The salt made it a lot colder. So,I got to thinking,why shouldn't it work with a ss pot? Just put salt on the ice surrounding the BK instead of water.
I may just try this next time.