Since reading the drop safety thing, I was looking at the SIG P320 mechanism and was curious about a couple of things. I was hoping someone familiar with the mech would mind explaining how certain things work. And I'm asking about a gun with no manual safety.

And I hope no one minds references to Glocks. I'm not much of a Glock fan, but most people understand how they work so it is a point of comparison.


On the P320, what keeps the sear in place when the gun is carried? Obviously the sear spring puts pressure on the sear to hold the striker, but is there any other mechanism or part that needs to be moved out of the way of the sear for the sear to move?

To provide an example, a Glock's crudiform trigger bar dingus means that the trigger bar (which acts like a sear) is not able to fall off the bottom of the striker until it and the striker have been pushed to the rear first. Is there any mechanism in the P320 that requires two separate movement to both free and then move the sear?


On the P320's striker safety, does that safety restrain the striker at full cock or does it allow the striker to fall to where it has less striker spring force?

I'm contrasting that with the Glock Pin Block that catches the striker just before the primer when the striker spring is completely relaxed.




What I'm wondering is essentially, could the P320 sear be "bounced" or otherwise jarred off the striker? On a hammer fired pistol the answer is usually "yes", but then the half cock notch or firing pin block prevents the hammer from actually firing the gun.

And if the sear was no longer in contact with the striker, what is the striker safety doing? Where does it end up intercepting the striker? How much striker pressure is the striker under when the safety catches it? What force is holding the safety in place?

In other words, if the sear fails for whatever reason, is the striker safety able to also act like a sear, launching the striker with full force if it also were to disengage? (I'm assuming it is also held in place by spring pressure.



Also, it looks like both the sear and striker safety work vertically. The sear pivots down, and the striker safety slides up from the pivoting striker safety lever. Is that correct?



I'm just interested in the technical details. I couldn't find a P320 firing animation, so I was hoping someone who has a P320 and is also mechanically inclined would be interested. This isn't some fanboy baloney.

Thanks.

Besides Bruce Gray, there are a couple of other SF members with a detailed understanding of the P320 internals. I'm not one of them.

I've seen one or two posts that I can recall. Can't remember who or when though. Might try a search.

Another question that would help me understand the mechanism:

Is it possible to "cock" the striker in the slide just by using the sear safety to lock the striker back in the striker spring compressed position?

SIG's official P320 video contains a cutaway animation starting around 1:55.

https://youtu.be/Y_qStEMQPts?t=113

Thanks for the video. I really don't understand what the striker safety does, since you would think it prevent the striker from moving forward from the striker housing, but the video at 2:02 shows the striker safety moving to the rear of the striker.

How does the striker safety block the striker? What is it catching?

The upper end of the striker safety engages a notch at the rear of the striker body.



After disengaging from the sear, the striker can move quite a distance in the housing before it would reach the point of hitting the striker safety.

quote:

Originally posted by gc70:
The upper end of the striker safety engages a notch at the rear of the striker body.



After disengaging from the sear, the striker can move quite a distance in the housing before it would reach the point of hitting the striker safety.

Very good! I take it that notch in the lower picture is pretty much at minimum spring compression, so the gun wouldn't fire if released from that point?

quote:

Originally posted by RX-79G:
I take it that notch in the lower picture is pretty much at minimum spring compression, so the gun wouldn't fire if released from that point?

Based on the appearance and purpose of the parts, that would seem to be a reasonable conclusion, although I have no way of testing to provide definitive proof.

IF, and it is a big if, the P320 is firing when dropped, I can see a sequence of events that may explain it.

The initial impact is jarring the sear off the striker. Before the striker gets to the striker safety, the rebound is just enough to throw the striker safety up just as the striker moves past it. It would require fairly precise timing, but if the gun hits at the right speed and mass, it would happen pretty repeatably because the impact creates the right "frequency" of cascading effects that perfectly match the striker speed.

Makes me wonder if this is why VP9s have rotating striker safeties.

The P320 striker safety rotates and is held down by a spring.

Yup. And the sear rotates and is held by a spring. But both appear to have more mass on one side of the pivot point than the other, so they aren't neutral to impacts.

Getting back to the mechanism, the newly minted drop firing video by TTAG has the P320 at the same angle as the original "pirate" video, but rotated 180°. One this wit dropping a firearm is that the bounce has considerable force - if you drop a steel ball on a steel plate, it will bounce almost as high as it was dropped from - higher than a superball.

So I think the drop firing is caused by the way both the sear and safety lever are sprung and are heavier on one side of their axis points, so inertia in a similar direction could affect either - just that it would have to be sequential forces in opposite directions - like a bounce.

However, other components could be responsible for one or the other release, or both. Anyone have a P320 that would like to play around? (No dropping!)

In the new Omaha Online video, they find that a reduction in trigger mass prevented drop firing:
https://www.youtube.com/watch?...si_VQsGA&app=desktop

The reason that most striker guns have tab triggers is because the trigger and the trigger bar on those guns both move in the same direction, so something needs to stop their combined mass from moving together. With traditional trigger bar arrangements, like the P320 uses, the trigger moves back and the trigger bar moves forward - like two similar sized kids on a teeter-totter. Gravity can't yank harder on one side than the other, so they normally balance out, which is why a P226 is drop safe even when cocked.

Omaha's tests make it appear that the trigger's mass is not being balanced sufficiently by the trigger bar's mass, so the trigger is 'winning' - like a really fat kid on one side of the teeter-totter.

Another possibility is that they should balance each other okay, but the Safety Lever (the purple cam in the animation still above) is also contributing its off center mass to the equation by removing its and the striker safety's resistance from the trigger bar. At that point the trigger's mass differential with the trigger bar's only has to overcome the sear spring pressure, rather than the sear and striker safety.


I have to wonder if the kind of CAD programs firearms makers currently use have avaiable the kind of physics modeling that would allow mass/inertia/gravity testing before production to avoid this kind of problem. Though I think some thoughtful scrutiny would have also worked.

Did SIG built the gun to be drop safe, or just pass ANSI drop tests? They certainly are not the same thing, but could be mistaken for the same thing by well meaning engineers.