I watched my father do this on a wee little vee spring (holds up cocking rod in Cashmore SLE) a couple of months ago. After reading Bailey's post above, I can see it was an amateurish job, but is working well so far. He used a propane torch and judging by color, annealed, opened and bent ends to reshape cold, hardened and tempered. First try he tempered to far (when tested with pliers spring lacked spring), so rehardened and retempered. In fairness to William Cashmore, I have a vague memory of making said spring under my father's guidance 35 years ago after fiddling with and breaking the original.
Inspired, last week I made a new top lever spring for my project gun out of a hacksaw blade. I shaped the spring hot. Took three tries, but it seems to be working.
I say go for it.
