Sig Sauer P320: The Swiss Cheese Explanation

In our previous examination of Sig Sauer’s P320 uncommanded discharges issue, a whole lot of commenters seem to get hung up on the screw, ignoring the methodology that Wyoming Gun Project laid out in his video. Well, it is a 40 minute video, and maybe he didn’t explain the preconditions for the failure mode he was trying to demonstrate well enough.

Well, here’s a 20 minute video by Shadetree Armorer that explains, in much clearer detail, the part failures the screw simulates before the loose slide come into play.

  • For legal reasons, he says to add “allegedly” every seven words or so.
  • “This is meant to be a summary with some connecting tissue uniting the whole so you can understand the big picture.”
  • “Despite what Sig may publicly claim about the P320, it relies on exactly two things to not go off, and the trigger isn’t one of them.”
  • “The first thing the P320 relies on is the sear. It is important to note that, unlike a Glock or even a 1911, there is no feature or device that blocks movement of the sear when the trigger is not pressed to the rear.”

  • “It is floating on two coil springs. These two coil springs and by way of geometry, pressure from the striker spring, are the only thing holding the sear in place.”
  • “The second thing that the P320 relies on is the safety lock, more commonly referred to as the striker safety or striker safety lever, which is held in place with a torsion spring. So, in order for a SIG P320 to discharge without a trigger pull, both the sear and striker lock must move, and those things are only prevented from moving by spring force.”
  • “The firing pin safety, that part was designed to be stamped. Someone in finance was like, ‘Hey, let’s save like $30 per pistol.’ So, a bunch of parts that were designed to be stamped end up becoming MIMed [Metal Injection Molded], which includes that striker safety. So, what’s the difference between stamping and MIMD in terms of safety and quality? With MIMing, once in a while, you might run into bubbles in the safety lever. If the bubbles break, then you have a problem where it shears off, the striker goes forwards.”
  • “With safety levers in particular, if there’s a wear issue, the striker goes forwards and the safety lever saves you a few times. There’s a possibility that it’ll break after a few instances of it happening. Out of the box, if you have a good one, the pistol should be safe, which is why the majority of 320s haven’t gone off. But if you have a bad one out of the factory or if you drop it too many times, then you might have a problem.”
  • This, by itself, is not enough for an uncommanded discharge. “You also need a sear issue.”
  • Next up: The FBI Ballistic Research Facilities report on a Michigan State Police P320. Quoting from page 29:

    Because of the inherent movement between the slide and frame, a third test of the striker safety lock was conducted. Approximately 50 attempts were made to determine if the striker would impact the prime case after manipulating the weapon while holstered. The weapon was pressed together and pulled apart at the slide and frame. Thereafter, pressure was applied to the frame and the sear manually released from the primary notch. The intent of the manipulation and pressure was to mimic what might occur to a holstered weapon during an officer’s duties, such as running, jumping, climbing, fighting, pressing a weapon against a wall or vehicle, or obtaining a master grip on the pistol prior to drawing, etc.

    BRF staff observed the prime case fired on nine attempts, with the primer indent measuring between 019 and 0026 of an inch with, an average of 023. While staging one attempt to allow another BRF staff member to observe the striker safety lock function as designed, the weapon was prepared and placed in the holster with no manipulation. A second staff member released the primary sear notch from the striker and the prime case fired, indicating failure of the striker safety lock.

  • “The important thing to take away here is that the striker safety in the examined firearm was able to be defeated by simply jostling the P320 in the holster, as would be expected to happen for any firearm carried in the holster throughout the day.”
  • Following the airman’s death, the Air Force released instructions on checking the striker safety in each gun. “The Air Force does not trust the striker safety lock either. They also mentioned specifically to check for proper assembly.”
  • “So, we have good reason to believe that the striker safety design is compromised and ineffective. Anecdotally, I have also heard reports elsewhere that it is sometimes assembled incorrectly from the factory, with one leg of the torsion spring being dislodged.
  • “I have also heard anecdotal reports that fouling such as carbon, unburnt powder and brass shavings can overwhelm the spring, and as a result the safety lever sticks in the upwards defeated position. My perspective on this is that the design seems to allow for a lot of surface area for fouling to build up when compared to the typical round plunger design.”
  • “There does not seem to be a singular problem with this safety lever. Rather, there are allegedly a lot of problems.”
  • “Why did SIG choose this design? Well, it is very compact and it saves having to cut a pocket in the slide for a striker safety plunger design like Glock, Smith and Wesson, and pretty much every other striker fired pistol use.”
  • The P365 doesn’t use safety lever design of the P320.
  • “The second thing that needs to happen for a P320 to discharge without a trigger pull is that the sear needs to release the striker. Now, you’re never going to guess. It looks like there’s multiple alleged ways for this to happen as well. And they can combine and get worse, just like the striker safety lever issues.”
  • “First, it seems as though there’s the potential for the takedown lever for large frame guns, that is 10mm and .45ACP, to get mixed up with the takedown lever for small frame guns. Whether this has happened in factory guns has yet to be seen. However, one of the most stalwart defenders of the P320’s honor, Grey Guns, has put out a notice stating that this combination of parts can create an unsafe condition.”
  • “I won’t get too into the weeds, but the take down lever is what allows the P320 to be disassembled without a trigger press. And it does this by lowering the sear via an arm. For whatever reason, Sig designed the large frame and small frame pre-P320 takedown levers to fit interchangeably. But importantly, the large frame takedown lever reduces the sear engagement in the small frame guns when it is in the assembled and ready to fire position.”
  • “The second way this can allegedly happen is poor surface finishes, or geometry of the interface between the striker and sear. Because nothing forces the P320 sear to fully engage in the way that the drop safety slot in a Glock trigger housing forces the Glock trigger bar to fully engage the striker, we are again reliant on spring pressure combined with a bit of geometry. However, should the geometry be off or a poor surface finish, or a burr be present in the sliding searsurfaces, these parts can get hung up, resulting in reduced sear engagement.”
  • “The FBI BRF’s report of the MSP320 that discharged in a holster found that one of the sliding sear surfaces had a ledge. And the US Air Force’s supplemental inspection criteria released on July 22nd specifically calls out the sear and striker assembly as areas to look for damage.”
  • “The third way that the sear and striker engagement can be reduced is by fouling or debris. That’s a bigger subject that we’re going to get to later because it affects all P320 pistols.”
  • “The important thing to note is that none of these problems are enough on their own to make the sear release the stiker uncommanded.”
  • “I was reminded of the Swiss cheese safety model by Gen Y Revolver Guy on Arfcom.” In which only when several problems occur at once, passing through different Swiss cheese holes, does the problem occur when all the holes (flaws) happen to line up. “That final piece of Swiss cheese in this situation, which all the issues I’ve covered combine with, is excessive movement between the slide and frame that seems endemic to the P320 platform. In particular, the slide can move up and down relative to the frame, which is enough to shift the sear engagement. And combined with one or more of the three aforementioned issues of incorrect takedown levers, bad sear surfaces, or firing debris, this can be enough for the sear to let go of the striker entirely.”
  • Now the part most immediately relevant to this previous post. “In these videos from Wyoming Gun Project, the loose slide to frame fit is demonstrated as well as the ability for that slide movement to release the striker when the striker engagement is reduced. It’s important to note that he set his P320 up to have reduced striker engagement by using a screw to pull the trigger to the rear a small amount past the wall in the travel after the takeup. And the takeup also serves to defeat the striker safety lever. So those two issues are simulated here while the third issue loose slide to frame fit is demonstrated.” Those who still don’t understand the purpose of the screw should read and reread that section until they do understand.
  • “It’s not simulating a screw getting stuck in the trigger. It’s a static and repeatable simulation of other known issues.”
  • Back to the debris issue. “The design of the P320 seems particularly susceptible to capturing environmental debris between the sear slide and striker. Indeed, these parts all combine to form a pocket. And if the pistol is carried muzzled down in a holster, the bottom of that pocket is a place where fouling and debris can accumulate.”
  • “Worse, there’s a gap between the frame and the slide directly above that pocket through which things from the environment can fall into.”
  • “This video from YouTuber Mischief Machine demonstrates that if the area is fouled with unburnt powder and brass shavings, the sear engagement can be reduced to the point that the slide movement will release the striker.”
  • Once Mischief Machine inserts the debris with the strike safety already simulated off, he gets the gun to discharge by tugging on the slide.
  • Again, the P365 doesn’t suffer from this P320 design flaw.
  • “I think that tidies up things nicely for this P320 saga. It’s pretty obvious what the problems are. The FBI and the US Air Force both seem to be on the same trail, and I honestly don’t think SIG has a realistic chance of fixing all the problems.”
  • “I think their only option at this point may be bankruptcy, which is why they are pushing so hard with the PR spin to gaslight everyone.”
  • Shadetree Armorer also points to YouTuber Dick Fairburn’s SIG P320 An unfolding Disaster, which I haven’t had a chance to watch yet (it’s another 40 minute video, and seems heavy on talk and light on illustrations).

    I had no intention of doing another Sig P320 post so soon after the last one, but the video was so informative on the (alleged) flaws, and so clear on things people seem to be getting hung up on, that I thought it was worth posting.

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    16 Responses to “Sig Sauer P320: The Swiss Cheese Explanation”

    1. Malthus says:

      “I think their only option at this point may be bankruptcy, which is why they are pushing so hard with the PR spin to gaslight everyone.”

      If it were done when ’tis done, then ’twere well It were done quickly..

    2. 10x25mm says:

      The MSP P.320 had evidence of serious damage which must have occurred prior to the incident. It also showed abrasion tool marks which suggest the incident was deliberately fabricated, in short, a hoax.

      The FBI Ballistic Research Facilities report on a Michigan State Police P320 shows an “abrasion” inside the trigger guard in its Figure 13. Quoting from page 14: “It was reported by MSP that the motor officer’s weapon impacted the ground during the transition program. However it is unknown if this caused the abrasion.”

      An FBI BRF technician used keys to discharge a P.320 (this pistol?) in the Alien Gear holster. See Page 20 of the report. They describe discharging the weapon in the holster, using keys, which created an abrasion entirely similar to the abrasion in the incident pistol noted above.

      This incident was another hoax, and the Michigan State Police announced on July 16th that they have fully adopted the SIG Sauer P.320/M18 pistol.

      Some 8 million pounds of metal alloy powder is transformed into mechanical parts by the metal injection molding (MIM) process each year in the United States. This amount to over 100 million parts. There are advantages and disadvantages to MIM parts, but they are generally made to much closer tolerances than stamped parts, even fine blanked parts. As to structural performance, they perform quite reliably. The process has a much better reputation than stamping in the engineering community and engineers are willing to pay a hefty premium for MIM parts.

      Anyone with a WW II P.38 is at risk of their stamped firing pins fracturing at their safety engagement lugs, despite Firma Walther spending six years on the firing pin design. It is an extremely common failure mode any why few firearms designers are willing to risk stamped parts in pistol firing systems.

      Firma Walther redesigned the P.38’s firing pin post war as a Swiss turned shaft and Umarex has been a leader in MIM adoption since they absorbed Firma Walther. There is also a very good reason the M3 SMG was quickly redesigned into the M3A1, without the stamped cocking handle. That stamped cocking handle had an almost 100% failure rate within 3 months of service.

      Stampings can perform well if properly designed and the tolerances are acceptable, but they cannot be said to be superior to MIM.

      The F.E. Warren AFB incident is now the subject of a criminal investigation. An airman is in custody for involuntary manslaughter in the incident. To understand the math here, this means that another individual was present and involved in the incident. This was another hoax.

      I do want to see more testing on the wear and debris possibilities, but none of the legitimate tests performed thus far suggest that either normal wear or fouling which could enter a fully assembled P.320 could cause an “uncommanded discharge”. No one has focused on this yet.

    3. Borepatch says:

      Stick a fork in them – they’re done. There’s so much here already that this is unrecoverable.

      The only thing I can think of is for them to post a detailed, repeatable video on what’s going on. I’d be very surprised if their corporate lawyers let them.

    4. Malthus says:

      “To understand the math here, this means that another individual was present and involved in the incident. This was another hoax.”

      All the weighty evidence heretofore presented is just an elaborate conspiracy to defame the storied P-320. Move on, people. There’s nothing to see here.

    5. 10x25mm says:

      “The first thing the P320 relies on is the sear. It is important to note that, unlike a Glock or even a 1911, there is no feature or device that blocks movement of the sear when the trigger is not pressed to the rear.”

      “It is floating on two coil springs. These two coil springs and by way of geometry, pressure from the striker spring, are the only thing holding the sear in place.”

      These two statements are flat out lies.

      The P.320 sear is hinged on a cross shaft at its front and propped up at its rear (called the sear tail) by a metal prop actuated by the trigger bar (which Thomele refers to as a safety bar in his patents). The sear prop resists 250 N (56 lbf) of downward force in my 9x19mm P.320, the force limit of my test fixture. So it probably resisted double or more force before parts breakage occurs. The sear is confined in an MIM housing which strictly constrains lateral movement. This is a very conventional sear system for a striker fired pistol.

      The two springs mentioned in these false statements only elevate the sear during the firing cycle, while the shooter’s trigger finger is still holding the trigger fully to the rear. The sear needs to be elevated before the slide returns, iin order to catch the striker sear surface and prevent full automatic fire or full striker travel without igniting the primer (which would disable the pistol). Once the shooter releases the trigger after the discharge, the metal prop actuated by the trigger bar returns to position and resumes full control over the sear tail.

      These two sear springs play no role in the P.320 when the trigger and slide are in their forward positions.

      You can see this in detail at ‘The Truth About Guns’ post authored by Jeremy S. on April 24, 2023:

      “Why Did the The Washington Post and The Trace Misrepresent the SIG P320’s Safety System in Their Hit Piece?”

      Alternatively, you can see this design in the Thomele patents. U.S. Patent 10,684,087 B2 “Handgun sear with multiple engagement surfaces” offers the best illustrations of the SIG Sauer P.320 firing mechanism components.

      Or you can buy a SIG Sauer P.320 and take it apart, like I did.

    6. Malthus says:

      “Or you can buy a SIG Sauer P.320 and take it apart, like I did.”

      We finally agree. The safest course of action is to leave this dog rocket disassembled after first taking it apart.

    7. Pod Hamp says:

      Does any here know if you can buy a Sig P320 chambered in 10x25mm?

    8. 10x25mm says:

      “Does any here know if you can buy a Sig P320 chambered in 10x25mm?”

      Yes. I pick mine up Wednesday.

    9. Malthus says:

      Ouch! SIG:Self Injury Gun.

    10. Malthus says:

      It is possible to incorrectly reassemble the P320, which may lead to the pistol firing simply by touching the slide. This is demonstrated in the “Gun University” video” below:

      https://m.youtube.com/watch?v=0lBTx1OHCP4

      It is similarly possible to incorrectly reinstall the gas piston and firing pin on a M-60 machine gun. Comrade Cartridge has earlier written in defense of that train-wreck, which would seem to indicate he is intrinsically drawn to problematic designs or it may possibly indicate a misplaced loyalty to GI ordnance…

    11. 10x25mm says:

      “It is possible to incorrectly reassemble the P320, which may lead to the pistol firing simply by touching the slide. This is demonstrated in the “Gun University” video” below:”

      Your latest idiot video demonstrates why SIG incorporated the safety takedown lever devised in Adrian Thomele’s U.S. Patent 10,724,814 B2 – “Handgun Safety Mechanism” in the P.320. When the takedown lever is out of home position in the frame, the striker safety lock cannot be disengaged. It is also impossible to insert a magazine, loaded or unloaded.

      Read the patent. You will become much smarter.

      This moron, who may be dumber than you, did not realize this because he did not use a primed case to ascertain whether the pistol actually discharged. He also has not read the patents describing the features incorporated in the SIG Sauer P.320.

      Your memory continues to fail. While the gas piston can be misassembled in the M60, the firing pin cannot. Only qualified armors work on the gas piston in M60 barrels now that safety wiring is SOP, and has been since the 1980’s. Any who misassemble the gas piston should be discharged from service. They are supposed to be experts. This gas piston issue only arose in the late 1970’s with the very low intellect VOLAR troops. Your intellectual equals.

      The other actual M60 problem is correctly assembling the grip frame pin retention clip. It can fall off when bent or damaged. The field expedient when replacement clips are not available is to deliberately assemble the clip upside down. Or replace the frame retention cross pin with a shear pin and cotters.

      I routinely got 100,000 trouble free rounds out of my M60’s. They are not MG.42’s, but they are lighter and more durable than the MAG when operated by competent personnel. You, of course, have not fired or maintained any of these three guns.

    12. Malthus says:

      “The moron, who may be dumber than you, did not realize this because he did not use a primed case to ascertain whether the pistol actually discharged.”

      He used an eraser-tipped pencil to demonstrate firing pin protrusion, a standard test with which you are obviously unfamiliar. You had charts, graphs and elaborate testing fixtures available for you to ascertain the root problem.

      He succeeded where you failed because you set out to prove the P320 critics wrong whereas he discovered the problem because he was humbly open to discovering the truth.

      Your self-validating rectitude is exposed as Pharisaical posturing.

    13. 10x25mm says:

      “He used an eraser-tipped pencil to demonstrate firing pin protrusion, a standard test with which you are obviously unfamiliar. You had charts, graphs and elaborate testing fixtures available for you to ascertain the root problem.”

      Primed cases are the gold standard. Pencil erasers are not.

    14. Malthus says:

      Withering criticism seems to be coming from all directions. Trigger Smart adds to the dog pile:

      https://m.youtube.com/watch?v=XACZxOOcDD8

    15. 10x25mm says:

      “Withering criticism seems to be coming from all directions. Trigger Smart adds to the dog pile:

      https://m.youtube.com/watch?v=XACZxOOcDD8

      He starts off with a reprise of the springs holding the sear lie. From my previous statement:

      “The two springs mentioned in these false statements only elevate the sear during the firing cycle, while the shooter’s trigger finger is still holding the trigger fully to the rear. The sear needs to be elevated before the slide returns, iin order to catch the striker sear surface and prevent full automatic fire or full striker travel without igniting the primer (which would disable the pistol). Once the shooter releases the trigger after the discharge, the metal prop actuated by the trigger bar returns to position and resumes full control over the sear tail.

      These two sear springs play no role in the P.320 when the trigger and slide are in their forward positions.”

      This click bait clown has not talked with any “gun engineer”. The P.320 sear mechanism is simple to analyze.

      Then he decided to attack torsion springs. Properly designed, made, and processed, they are fully the equal of coil springs and no more difficult to manufacture. Lifetimes exceeding one million cycles are the norm when properly designed and made. Smaller torsion springs are often made from the same wire, on the same winding machines as coil springs.

      You and these other click bait clowns would greatly benefit from a course in Mechanical Design. MIT OpenCourseWare offers a free course titled ‘Elements of Mechanical Design’. Its description:

      “This is an advanced course on modeling, design, integration and best practices for use of machine elements such as bearings, springs, gears, cams and mechanisms. Modeling and analysis of these elements is based upon extensive application of physics, mathematics and core mechanical engineering principles (solid mechanics, fluid mechanics, manufacturing, estimation, computer simulation, etc.). These principles are reinforced via (1) hands-on laboratory experiences wherein students conduct experiments and disassemble machines and (2) a substantial design project wherein students model, design, fabricate and characterize a mechanical system that is relevant to a real world application. Students master the materials via problems sets that are directly related to, and coordinated with, the deliverables of their project. Student assessment is based upon mastery of the course materials and the student’s ability to synthesize, model and fabricate a mechanical device subject to engineering constraints (e.g. cost and time/schedule).”

      You would also benefit from their Strength of Materials courses, which MITOpenCourseWare refers to as ‘Mechanics of Materials’

    16. Nichevo says:

      I owe you an apology, 10mm. I always thought that you were a cold, unimaginative, tight-lipped Russophile. But you’re really quite emotional, aren’t you?

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