I was able to obtain our pistol that was related to our ND/AD and I took it down to the individual parts......which I had never done and this pistol was factory fresh with a build date of 10/2017. I entered the s/n into Sig's website "upgrade" checker and it came up good to go per Sig.
However.......
Dual sear springs were crossed and not putting correct pressure up on the foot of the striker
For lack of a better term, apparently this is an older style sear that lacks the nipples or posts that the springs slip over to keep them aligned.
It has dimples instead....and apparently, whoever assembled this thing in 10/17 did so in a hurry.
This is the spring that Sig no longer installs in recent builds. I feel certain that I now know why.
This little spring, which is the spring that retracts the lever that lifts the striker block, was a little hosed up. My thoughts are that the striker block lever was "stuck" in the upward position, with a striker foot not held by proper dual spring tension, and when our guy holstered, when his pistol clicked down and seated, the striker slipped from the sear and fell forward....discharging the HST round.
I have taken several apart from that same general time of year this one was build. They all have the newer style sear with spring posts instead of the dimples.
I'm 90 percent sure this discharge wasn't his fault. We assumed garment on the trigger but now I'm leaning towards the gun. I plan on sending Sig a certified letter this week as I need a replacement sear for this gun as well as any others I come across that have the similar, older style sear.
We have pulled them from duty and most have qualified on other pistols. We will see where it goes. I'd like confirmation from Sig that the fix is to simply remove that striker block lever spring from each copy and to ensure they have the most updated sear. If that's the fix to make them safe, I can do that for nothing for most of the guns we have.
I also appreciate this thread and they way everyone conducted themselves.