Now & again someone discusses making springs. I've been a metallurgist since JFK was messin' around in the White House, & involved in steel heat treating. However, the only springs I personally made were 1/3 scale miniatures which I cold formed of Swedish spring steel. That doesn't necessarily qualify me to give practical advice that a gunsmith might understand & find useful.
All these years and I never knew that Kit Ravenshear had written such a wonderful manual on making springs, Simplified V-Springs, A Guncraftmanship Manual It is available from Dixie Gunworks. Not having thoroughly read their magnificent catalog, I found mine browsing abebooks.
Ravenshear tells exactly how to deal with springs, both formed from spring steel and castings. I looked through critically, not with high expectations. Although my terminology might be different here & there (thus maybe not too clear . . .) I would say he is spot on, everything he says is technically correct and practical.
I would suggest if you are going to follow his advice that you follow it EXACTLY, as to quenching and tempering a spring. Do just as he says, do not decide there is a more convenient way for you. Use the steel he says to use. Tempering by "burning off the oil" is one subject that comes to mind. Follow his recipie religiously and you should be happy. Short-cuts = gotta make a new spring.
This fine booklet was first published Spring 1990, then reprinted in 2010. If you do any shop work involving springs, get this book.