I can't explain your problem, but I always stay with the std. S&W mainspring. I have changed the Trigger Rebound Spring to 13# Wolff springs on three of my older Smiths.....M-17 K22, M-67, M-10 2" carry piece. I get a smooth, lighter trigger pull, and no ignition problems, with any type of ammo. It will shoot anything!
I feel that it is light enough for my purposes. The K22 has also had an action job at S&W. It has a really sweet DA trigger pull, and you just have to touch the trigger in SA, to make it shoot!
I shoot the K22 DA, mostly. The SA pull is so light....it's scary!
You don't even touch the trigger, before you're ready to shoot. Bob