The P320 Problem

I began this site by poking Mossberg for posting stupidly accessorized shotguns on their social media. I guess I’ve made it up to them by recommending one of their (naked) products as the first “great gun” in the category. Well, all that seems a little tame because now I have to risk poking a bigger bear, and harder. We all know what this is about: The Sig Sauer P320, and its alleged safety issues.

Let me get the apology in first. I have nothing against Sig Sauer, its products in general or its people. From the earliest days in Switzerland, via Germany to its present day position as one of the USA’s great gun brands, they make stuff I like. I’ve put this post under “great guns” too for a reason. The P227. A P220 in 45 or 10. A P226 in 357 SIG (yes, I like the 357, we’ll get to that another day). The list of great and innovative, and safe guns made by this company – including those made in the USA – is long.

Is the P320 unsafe?

So, what the hell is wrong with the P320? Is there anything wrong at all? Well, we know about the trigger issue a few years ago, and that it’s been fixed. Sig wouldn’t be the first company by any means to discover a problem that is both highly unlikely, yet absolutely needs to be fixed. People who like guns care (or should care) a lot about safety because they take on a life and death responsibility by being armed. Sig Sauer took their responsibility too and did it right: if you weren’t aware. the original trigger blade had enough mass to move under its own momentum, in one extreme and very particular drop/strike scenario. Sig reduced the trigger mass and replaced all the old ones free of charge. It has never happened again.

But, unless you’ve been living in a cave you’ll have heard of more recent alleged issues. The P320 is apparently “firing by itself”. Well, damn.

So are people running away from Sig Sauer in their droves? According to gunbroker.com the P320 was their best selling item in 2022. As of the last figures I saw, it’s dropped to second, behind another striker-fired Sig Sauer pistol, the P365. If they’re hurting, it could be worse.

As an upstanding member of this community with a small god complex and a relentless thirst for knowledge, I’ve done a little reading and some tinkering, and worked some things out. First, let’s eliminate the obvious: keeping a firearm loose in your purse or bag is the absolute definition of being a dumbass. If it shoots you, you deserve it. If it shoots someone else, you deserve what you get. No manufacturer can legislate for truly wilful dumbassery. If it’s not in your hand, the trigger needs to be contained in a holster or in a case. A few of these instances have led to some noise by the idiots involved but they are a distraction. Forget them.

Then there are the others, and this is the meat of the issue. The people saying they had their P320s safely holstered, hands off, no obstructions, and they just fired. Well, that also sounds far-fetched, but it’s believable enough for there to be a class lawsuit or two in progress. Milwaukee’ PD’s police union have had a cluster of incidents – they seem to be suing the City rather than the manufacturer because maybe they know something about which one can afford better lawyers! But more than twenty other lawsuits have happened around this issue.

A P320 really did fire without the trigger.

And then there’s this: if you’re not renting Ted Kaczynski’s cabin, you’ll have seen a video of a cop’s P320 firing a round without anyone’s hand near it. There has been a mixed reaction to this. Predictably, some fans of other brands and makers have pointed out their supposedly better safety records, without much statistical analysis. “Well that’s why I have a Glock, S&W, etc.” is getting boring. Others are downloading with a whole stream of alleged crimes by Sig Sauer, questioning their Government contracts, and generally dumping on the brand as much as they can. Sig is getting a hard time even if sales are still good.

On the other side are the fanbois. Hundreds of thousands of P320s are owned and loved across America and beyond, and nobody likes to think they bought a dud. The fans are out in force. YouTube agitators are camped out on either side. A particularly stringent defense from “The Yankee Marshall” is worth a look. He’s a guy I find entertaining to watch and says some smart things. In this instance though, a quick referral to the comments section explains why his “it wasn’t in the holster correctly” spiel looks a little desperate (and just wrong). I would only add that he defended the drop safety issue before the trigger recall too: fortunately Sig took it more seriously, as they should.

Neither you nor I were there in Montville, CT, or on those occasions in Milwaukee,WI when similar things are supposed to have happened. But at least in this video, we can see that something did happen. A Sig P320, correctly and securely housed in a quality tactical holster, fired a round without anyone touching the trigger. We know it’s not a drop safety issue – that’s been resolved, and it wasn’t dropped. We also know that two officers bumped briefly into each other when the shot was fired. So, how did it happen?

How a P320 safety works

Before we speculate as to what happened, a little lesson on how a P320 doesn’t fire. It wants to. Like any striker-fired pistol, the striker is held back against a spring, waiting to be released. If there is a round in the chamber, you’re ready to fire. The spring is compressed, the energy is stored. A small movement of the new lightweight trigger and it the striker is released, flies forward to hit the primer in the cartridge, and that’s “bang”. A striker-fired pistol with one in the chamber is much liked a traditional pistol with the hammer cocked. The mechanism that wants to fire is ready and waiting to be released.

Are all striker-fired pistols unsafe?

Is that fundamentally unsafe? Would you carry a revolver with the hammer back? Or a 1911 cocked but not locked? Or a P22x with the hammer back for that matter? Probably not. It would feel unsafe. So, striker-fired pistols have safety mechanisms, and they’re all different. I want to give a shout out here to a great channel on YouTube called “Sig Mechanics“. I don’t know who this guy is, but he patiently takes things to bits and shows in detail how they function. Rather than drawing too many clumsy pictures, I’m going to show you with some shots grabbed from his videos. There are two things that stop a P320 firing until you move the trigger. Actually three, but the third only matters if the slide is out of battery, which wasn’t and isn’t the issue.

1. The Sear

First, the sear. The sear is the moving part between the trigger bar and the striker (or hammer in other pistols). The spring is pushing the striker towards the cartridge, while the hook-shaped rear of the striker is held against a raised edge on the sear. As you move the trigger, the sear rotates to a point that the hook slides off that edge, and the striker is pulled off the sear and propelled towards the loaded cartridge to strike the primer. In this video, Mr Mechanics is actually demonstrating an additional safety feature – a second ledge on the sear that will hold the striker back if the main ledge is worn away through use. But as he shows, it won’t get in the way before that happens, so it’s irrelevant to our question: we can assume the self-firing P320s had sears in good shape. Take a look:

As you can see, if not from the picture then I hope from the video, the distance by which the striker overhangs the ledge on the sear is pretty small. Mr Mechanics says “about one millimeter”. That’s not unusual. Any cocked pistol has a striker or hammer hanging on the small edge of the sear, just like this. In the video, Mr Mechanics tries to push the striker off the sear manually. It’s not that easy – the striker is well contained in its housing without any play and doesn’t move up off the sear. To release it, the sear needs to move down – that’s what the trigger and trigger bar do. Still with me? Thank you.

2. The Safety Lever

Just in case something happens to the sear and it releases the striker, there is a safety in place. Again, this is standard on pistols. The striker safety needs to be released when you move the trigger to the rear, by a safety lever attached to the trigger. There are actually two levers that interract: one attached to the trigger in the fire control unit (more on that in a moment), and one attached to the striker assembly in the slide. Take a look again at Mr Mechanics’ excellent video, and the picture:

Again, it’s easier to see in motion in the video but the picture shows the end of the safety lever that has pushed up off the retaining notch in the striker. You can see lower down in the picture that the hook on the back of the striker is also well clear of the sear. Moving the trigger rearwards simulaneously rotates the striker safety lever upwards just a couple of millimeters, and rotates the shelf on the sear downward a few millimeters relative to the striker. With the safety lever up out of the notch, and the sear ledge then moving downwards off the hook-shaped rear of the striker, the striker is released and the striker spring drives it forward against the cartridge primer. Got it? Phew!

Without rearward movement of the trigger, the safety and the sear stay where they are, and hold the striker safely in place.

At least that’s what’s supposed to happen…

Somehow, the striker inside a working and well-maintained P320 pistol, held securely inside a strong and rigid holster, with the trigger completely covered and (despite what the Marshall wants to think) attached to a perfectly competent peace officer, was released and ignited a cartridge. That is the allegation. I want to show that is possible and demonstrable.

There is not much inherently different about the safety approach in the P320 and other pistols. Glocks, some S&Ws, Springfields etc., all have a striker retained under tension by the sear itself and some kind of additional obstacle that is removed only by operating the trigger. Some of those have an extra lever in the trigger blade that operates the safety, so that only a full fingertip on the trigger will operate both the safety and the sear. Many striker safeties involved a small plunger on a spring that pushes into the striker like a nail until withdrawn by the trigger movement. Sig’s version of the safety is not particularly strange. It is simple and mechanically efficient, especially if you want to keep a nice clean trigger pull.

So why is this happening to the P320?

There is something special about the P320. It is designed to be modular. Glocks famously allow easy calibre changes with just a different barrel of the same external dimensions – precise fitting is not required in the same way as, say, a premium 1911. The P320 does that trick too, but goes one further: the entire functional assembly of the lower part of the pistol – the fire control unit or FCU – pops easily out of the frame and into different ones. Long or short dust covers, long or short grips for different magazines, different shapes for different hands and plenty of after-market options. The P320 is the Barbie pistol to dress up as you like – barrel, slide, frame and that’s before any accessories. At least three different calibers immediately from the same fire control unit. It’s a great setup.

Is there is trade-off though? Being easy to take apart necessarily increases tolerances. Here’s another video from the Sig Mechanics guy that addresses a non-issue complaint by some owners. It’s not a safety issue but it reminds us of one thing: The slide assembly that contains the barrel, the cartridge in the chamber and the striker assembly, then the FCU that contains the trigger assembly, then the frame on which they both sit, are all independent assemblies.

Why might that be an issue? The phrase is “tolerance stacking”. Some time ago, the US Military discovered that its most used weapon, the M4 automatic rifle, could fire when it wasn’t supposed to. A particular and predictable set of circumstances could lead to its not firing, then firing unexpectedly. There was no problem with any particular part; everything was within the correct specification. All those individual tolerances were good and precise. The problem was that with a certain number of moving parts, in certain combinations and positions, all those tiny tolerances added up to a big enough error to make a problem.

Back to Sig Sauer and the P320. As the pictures and videos show, the difference between the striker releasing and not releasing is a millimeter or less. That’s normal for the sear dimensions. For the safety lever hanging by less than half a millimeter, the room for error seems small. Even so, of hundreds of thousands of P320s (and P365s, the new number one seller that seems to have a similar setup) are not all firing unexpectedly. A firearm is a precise instrument. As Mr Mechanics showed in the first part of the video, the striker is held very securely with no play and can’t be pushed up off the sear easily.

The problem that we are finally getting to is this: the striker and the striker safety lever are in the upper (slide) assembly, and the sear and the trigger safety lever aren’t. How much room for movement is there between the FCU in the frame, and the slide assembly? A millimeter, maybe? There shouldn’t be. Mr Mechanics’ second video shows that once a magazine is in, everything seems to lock up nice and tight. But every machine has its limits, and a cop in Montville, CT showed what they are.

P320 vs Cop

I like cops. I have a cop in my family. I don’t assume (like the Marshall – really?!) that cops try to accidentally shoot themselves as a back door method of gun control. But I do know is that much like soldiers and sailors, if something can be broken then a cop will find an ingenious way to break it. Bumping it off another cop in this case certainly didn’t help. Neither did his department’s choice of equipment. They were wearing a brand of hard shell holsters on a rotating mount that sticks the pistol a couple of inches out from the body. There is no thumb break to mess with, the pistol is held inside by a hard and closely-molded polymer box under tension against a screw. It also has a light on the end of the frame.

It is no secret that I think weapon-mounted lights are a dumbass trend, and especially irresponsible for cops’ handguns. I also don’t like these tacti-cool Robocop-looking holsters much. They bump into stuff too easily and are an invitation for bad guys to try to grab the pistol. Neither are the issues I need to talk about now. Actually, it might just be too good a holster.

To guard against someone snatching a cop’s pistol, the holster keeps it in place real tight. It’s a very popular holster system (there are a couple of different brands, not important which this one is) for cops and security types. If you ever hear someone draw from one, you know it’s really in there and takes a good firm vertical pull to extract. So if the P320 was in such a safe place, why did it fire?

Donuts and torque

If you look at the holstered P320 or most holstered sidearms, the grip is pretty much the only visible part. Here’s a simple series of events:

1. Cop 1 and Cop 2 collide (light blue)
2. Combined cop energy deployed against butt of P320
3. Force directed towards Cop 1 through frame of P320 (gray)
4. Polymer frame moves towards Cop 1
5. Frame pushes magazine (orange)
6. Magazine secured by FCU (gold) at top end
7. Bottom of magazine continues to move, creating torque effect
8. Rotational effect begins with magazine acting as lever on FCU
9. Slide (black) containing striker (red) anchored by hard holster
10. Weapon-mounted light prevents slide assembly twisting in holster
11. Rotational force on FCU alone stresses tolerances of frame integrity, FCU/slide alignment and frame rail rigidity
12. As integral parts of the FCU, the sear and the trigger safety lever rotate
13. Unlucky for some. The FCU is levered away from the slide assembly sufficiently to lower the sear by one millimetre. Maybe.

Yes, no, if and maybe…

Well that’s clear then, is it? The FCU twists in place against the slide and the front of the frame, that are held in place by the holster’s death grip on the slide and – helped by the light – the front of the frame. Enough force is applied momentarily to pull them slightly apart and hop the striker off the sear. But what about the safety? That’s a little more tricky to explain.

If it were the striker rotating clockwise, it could easily slip under the safety lever. But then it would be more firmly on the sear. If you take off the backplate, you can see the sear move along with the FCU. What you can’t see is the lower safety lever on the trigger. That has to rotate backwards just a shade to engage and lift the striker safety. How or if that happened remains an open question, but here are a couple of things to consider:

a) the striker safety overlaps the notch by a fraction of a millimeter

b) it is designed to disengage fractionally before the sear releases

c) the torsion and/or shock applied to the grip/magazine/FCU axis would not have been perfectly in one direction throughout the assembly

The mechanism by which the striker is disengaging from the sear is clear. Releasing the safety lever is less clear, but takes less distance and looks like an inherent weakness.

Maybe the impact alone just jiggled the safety bar out of its notch. Maybe pulling the sear down manually via the body of the FCU actually moves other parts of the trigger mechanism enough internally to move the safety lever by that tiny amount necessary. Maybe rotating the flat surface of the trigger safety lever against the flat surface of the striker safety lever is enough to lift it off the notch. What happens in there cannot be seen without a transparent pistol. But..

Here comes the bomb…

Either way, it can be replicated. Please make sure your P320 is empty! Lock the slide gently in a vise (use a cloth, don’t scratch it), just forward of the ejection port. Insert an empty magazine. Rack the slide by pushing the frame down against the vise. Please check again that there is no round chambered.

If you really want to be clever, replace the backplate with a pin or something like the Sig Mechanics guy so you can see (and film if that’s your thing) what’s going on with the sear. Or just leave it on, the result is the same.

Now bang that butt with the heel of your hand from right to left. Use a plastic mallet. Try bumping heavy stuff into it. If you’re a strong guy, try just twisting it around with sudden intense force with your hand. Sooner or later, your jaw will drop, along with the striker on the P320.

Well, damn.

(To be continued…)

English Al

P.S. Let me know how you get on. And really, empty magazine empty chamber. Check again. Don’t be a dumbass.