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Got out the ruler and dial-calipers and attempted to see what's what with the Sigma SW9V.
There's no direct way to measure sear engagement, so I had to measure from point to point to point to point...
Compared with FuzzyGeff's Sigma SW40F, the sear drops almost the same distance.
From 0.170" at rest to 0.096" with the trigger pulled for the .40.
From 0.169" at rest to 0.100" with the trigger pilled for the 9mm.
Pay attention to these thousandths, they add up.
The striker stud stands proud of the belly of the slide 0.229" on the .40; 0.207" on the 9mm.
Going all round the world to see where things overlap...
The .40 has 0.071" of sear engagement and the stud clears the dropped sear by 0.004" when it flies.
The 9mm has 0.022" of engagement and clears the stud by 0.047" when it's dropped.
The all round the world method of measuring this likely introduces errors at every one of the five points to get there, because the taller striker stud from FuzzyGeff's gun will not trip in the nine, despite having a calculated 0.044" engagement and 0.025" gap with the trigger pulled.
With the slide end-plate off you can see what's happening. The 9mm sear rotates the .40 striker as it's pulling it back, that increased the engagement by 0.007" making it 0.051" engaged plus it pulls it down at least 0.020" because it's galling into just one side of the stud (checked the scraping with a Sharpie) instead of riding smoothly against the face.
0.027" of increased stud protrusion is just enough to keep it from firing.
You can, sometimes, get the striker to fall by giving the slide a good whack with the trigger pulled.
If 0.022" of engagement is enough, then I can quit tinkering with the knowledge that I unfucked the previous owner's tender mercies.
If it's not enough, well, I'm bidding on a replacement striker and my measurements tell me that I shouldn't have to take much off at all to get it to work as long as I keep things square.
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