I have exhausted what I know....

[LRB]

Harden as usual, then use the molten lead to temper (same settings I cast round ball) then air cool. I have talked to a few that water cool after minutes in the lead. It needs to be long enough for temperature to be equal through out. I hang it on a piece of wire

The only purpose of water cooling is to let you get back to work sooner. Just to on the safe side, I would suggest the air cool until the steel is around 400°f. When tempering knife blades water cooling does no harm because the temps are normally well under 500°f With spring tempering being up around 750°f, I would wait a couple of minutes before dunking in water, although I doubt any harm would be done, better to be cautious after taking the time to shape a spring.