The thumb safety blocks the trigger bar's movement only. It does not block the sear's movement. The potential drop safe (or lack thereof) issue is from the sear releasing without the trigger being pressed. If a particular gun has the combination of parts, poor QC, and bad luck that will let the sear release uncommanded, then it would not matter if it had a thumb safety or not.
That said, the issue appear to be isolated to a particular date range and set of parts that lwt16 has identified. The first few pages of this very thread isolates the suspected parts and date ranges. Pay particular attention to comments from lwt16.
This thread has some good information about the inner workings of the P320 before and after the "voluntary upgrade program": https://pistol-forum.com/showthread....-safety-issues. Pay particular attention to comments from Tom-Jones.
I don’t know if it fits here or not but I have a few pictures of the internals of a new .mil M17. If it adds to the discussion let me know and I’ll add them.
“If you know the way broadly you will see it in everything." - Miyamoto Musashi
People are talking about how mamy sigs were sold, didn't glock sell 1 mil. 19X in a little less than a year? With how many people buying guns now, i don't know if 1 million guns is the benchmark it once was
I'm definitely interested. I finally have my hands on a manual safety FCU from AB Prototype, though I don't know if it differs from the M17/18 in a meaningful way.
There also seems to be a lot of confusion about how the manual safety on the 320 works, which makes sense given the rarity. Some pictures would be nice.
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Smart folks would do well to pay a LOT of attention to what psalms144.1 wrote back in post #131:
"it's damn near impossible to know what you're getting UNLESS you're getting a DHS contract pistol...........in a world of Gen5 Glocks, CZ P10s, M&P 2.0s, APXs, VP9s and 1911s, I wouldn't put my money or my safety into one (Sig 320)..."
Facts matter...Feelings Can Lie
Again, I'm no engineer, so I might be wrong as well, but my takeaway from reading Tom-Jone's, lwt16's, and JonInWA's comments in this and the other threads over the last couple of years is that the internal safeties can be defeated with inertia on the 320. The trigger moving in the videos is in some ways an artifact of the safeties being defeated.
I was/am confused about this as well. Confused enough that I pulled some bullets and started dropping my TDA guns in single action with primed cases in the chamber to see if inertia could pull the trigger and defeat the internal safeties on those guns as well. The triggers are heavier and the force/distance needed release the sear is less on those guns than on the 320. If the hammer fell, it always fell to half-cock. The primer never detonated like we've seen with the 320. I think something else was/is going on with the 320.