Randall is a good gunsmith, so this is stolen from another site, I am privileged to have had Tim La France having done my 1911 CC carry and Randall's explanation makes sense to me as a 1911 guy. Sure looks like the P320 thumb safety needs to bear against the sear like the P365, having dinner tonight with MSTN and will ask him his take.
Begin Stolen explanation,
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"Due to the nanny-rule against the word C-O-C-K, the little
appears a lot below in my technical explanation:
If we used the Glock safe action as the "standard" to compare against, the reason the P320 is so sensitive to going off is that the striker is fully
ed at rest.
Glock strikers are only partially
ed (to the point that if they DID slip off the trigger bar and fly forward), the striker does not have enough stored energy in them to reliably set off a primer.
The vast majority of striker fired guns work much the same way in that the striker is not fully
ed until the trigger is pulled.
The act of pulling the trigger also includes finishing pulling the striker back and storing more energy into the striker spring just before it's released.
Because of this, it's not possible to make the trigger pull of most striker fired pistols as good as a hammer fired pistol.
This method of safety has worked well for Glock and the other striker fired derivatives on the market.
The striker being fully ed means that all it takes to fire is for the sear to release the striker.
By eliminating that (Glock) safety step of having to pull the striker back the rest of the way to fully energize the striker spring, the Sig trigger pull is more like a hammer fired pistol such as a 1911.
That better trigger pull is WHY the P320 is so well liked over the longer/heavier (safer) trigger pull of the Glock.
So what you have in a P320 (without out a manual safety) is basically a
ed and unlocked 1911.
Do you know anyone that would carry a 1911 loaded,
ed and unlocked?
I don't.
In competition, we all start with a loaded chamber, hammer
ed and the manual safety engaged.
In the 1911 design, the manual thumb safety directly blocks the sear so that the sear can not move until the manual safety is disengaged.
In the P320 design, the manual safety does NOT block the sear from moving.
This is the primary issue I see with the P320 design, especially when you do not have a manual safety to keep the trigger bar OR the sear from moving.
The P320 manual safety blocks the trigger bar from moving and disconnects the trigger bar from the sear.
So because only the sear springs are keeping the striker
ed when the manual safety is engaged, it only takes a good jarring to cause the sear to release the striker.
This amount of jarring required for the sear to release changes by using non-standard parts such as reduced power sear springs or aftermarket sears.
There are other safety features in the P320 design to keep the striker from falling when the trigger is not pulled, but these safeties can be nullified when you introduce adjustable triggers or trigger bars to further reduce trigger travel and keep the trigger in a perpetually-pulled state which is bypassing the striker safety to make the trigger pull even shorter.
You might point out that the P365 striker is also fully
ed but P365's do not randomly fire.
This is possibly because the P365 is newer and not as widely adopted into service pistol roles like the P320 so there are simply fewer chances for them to malfunction.
Also, there is a very important difference between the P320 and the P365 manual safeties.
The manual safety on a P365 directly bears on the sear just like a 1911."
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