Wow, I don't quite know where to start here....
1) Springs break. Casting flaws, improper care, improper tuning, wood interference, whatever, springs break. That is why we offer a lifetime warranty on them. Most of the time folks don't ever have to use this warranty, especially on the smaller locks like the Silers, but occasionally it happens. As Dad stated to Finnwolf have two break is very rare, but it can happen.
2) As was also stated to him, without us being metallurgists and having high dollar metal testing equipment to run tests on the springs that broke we CAN NOT give any further explanation without seeing the lock and cycling it. It's not a trade secret we are trying to keep here, we just can't tell. Not to mention, it's a free replacement if it breaks, keep a spare in your shooting box and if/when one breaks you have an extra and can keep shooting while we send a new one back to you.
3) For all of you that want to jump on the 'it's not tempered correctly' - since we heat treat in batches of 200-400 at a time then we should be getting back 200-400 broken springs. Haven't seen them. Now since we did not build this particular lock it is possible that the springs were ground or worked in a way that changed them, but from looking at the one broken spring we saw nothing to indicate any problems.
4) We have offered to work on this lock - period. Without being given the opportunity to see it, check is architecture, and cycle it we can do nothing more than what all of you have done on the thread - speculate! And yet, here I am having to make a post when I can not answer it any better than we did over email because we have yet to see the lock.
I like Zonie's post about it possibly riding up into the tumbler shaft, that could be a possibility and something that we could notice if we'd been given the chance to look at the lock.
Please understand with what I am about to say is not meant to sound bad, but is going to be stated as what I deem the truth - grain of salt included.
Finnwolf's problem is he's had two main springs break over a 5 year time frame. He wants to know why, and yet has stated himself that he can not understand much of the technical information Zonie suggested nor will he send the lock in for inspection. So what exactly is being asked here? NONE of us can tell him a correct answer without having all the parts in front of us, inspecting both broken springs and cycling the current lock for technical problems. Seems to me this thread can do no more than serve as a complaint session.
Finnwolf, if you want to have trust in your lock, then have enough trust in the designer to send it back and let us look at it. We want nothing more than to have satisfied customers - please give us the opportunity to make you one.