Just thought of something which may help, if all is well with the rest of the mechanism and the spring can be re tempered, an old gunsmith told me to blaze the spring twice before trying it, his view was that it's better to fit a weak spring which would just bend if it's not hard enough rather than try one that's too brittle and may well snap. A weak one can be bent back to shape and hardened again where as a broken one has to be made from scratch.
I've only made one vee spring and it worked fine after two blazings , I'm definitely not an expert and while writing this it struck me that it's probably a job for someone who knows the task inside out.
Probably not much help but I thought I'd mention it.
