Lightstrikes or No stirkes on primer..?
...
If you're seeing some kind of primer strike but no discharge, then I'm thinking it's your main spring more so than the firing pin a/o spring is at fault.. I mean, if sent back to Sig and they tested it, fixed it, passed it, then it leaves me to think "main spring problem" and it may be just too weak.
Not sure, but IF they lightened up the trigger pull, or someone else, beforehand did, then it may be a nice, light, DA pull, but too weak to send the hammer hard enough against the firing pin or is just wearing out from use.
IIRC, Factory main springs are 24lb, but you can also call Wolff Springs and, like I did, order one of his main spring kits, to lighten up the DA trigger pull, as they come in different groups, the one I got started with a 20 or 21lb main spring down, 19, 18, 17lb, 16, to a 15lb main spring. I went with the 17lb main spring and have had no light strikes, thus far, thru some 4000 rounds of 40cal with a very smooth, light DA pull with one of my P229's
Luck,
Ls
Ps.. one can replace them, rather easily, using Sigs DVD Armor video as a guide which covers most P series, the 228 for sure. When ordering them from Wolff, one needs to know whether, and my bet is, it has a long main spring, or a short main spring.. aprox: 2" long spring vs 1" main short spring which he needs to know.