The OP was referring to a 'FLINT MAINSPRING". I consider that type to have a big curving hook rather than the claw type Mr. Roller is famous for. And I agree that the hook must be forged first on this type of spring.
For a flint mainspring, I like to start with material that is a little thicker than the finished spring will end up. When you make the bend, the forging process will diminish the thickness of the metal on each side of the bend. Also, on mainsprings from period pieces, I noticed that there is double the thickness of the leaves in the bend itself. Otherwise, the spring works too much through the bend and not in the leaves. So starting out with stock that is too thick will leave you with metal to dress down to the desired dimensions.
Further, it is my understanding that the hardening and tempering process which makes a spring work, aligns the molecules of the steel parallel to the leaves and the edges of the bend, like the pages in a book being bent around double. Otherwise, the molecules when just harde3ned and prior to tempering, are like sand with no structure that would lend itself to being bent - like a piece of glass.
I'd love to hear from a metallurgist who actually knows what he is talking about, rather than relying on memory from my youth.
