I looked at How to Make Springs. They have a table for stress relieving, but nothing in it comes up on my monitor. Anyway, if you do make your own, stress relieving is necessary. I made some springs similar to yours that were both extended and compressed in service. They would take a set both ways so the rest position depended on which way they had been last. I pushed and pulled on them until I got them back to the proper free length, then baked them. After that, they performed exactly to the specs in the ASTME Tool Engineer's Handbook. Thinking about it afterward, I should have realized that when you wind a spring, much of the wire is stressed past the yield point. If it wasn't, the wire would stay straight. Any deflection afterward will push some of it past yield some more and it will take a new set.
My springs were close to the size of yours and I wound them on 14 1/2" South Bend lathe running in backgear. Once I learned to make the starts and ends and got the diameter right, it was simple.
Bill