If every degree on the X, Y, and Z axes is a data point, there are over 46 million potential orientations in which to drop a firearm. Unfortunately, the SIG SAUER P320 has shown an unacceptably high potential for firing when dropped on a hard surface in at least one general orientation: on the back edge of its slide. SIG refers to this as a “negative 30 degree angle” and agrees that the P320 has shown a specific vulnerability to it. Below, we’ll answer why this is the case and present SIG’s solution.
The Physics:
Objects have mass, and mass has inertia. That’s an object’s propensity to fight acceleration (any change in velocity). An object in motion wants to stay in motion. An object at rest wants to stay that way, too. A trigger is an object; an object with mass. And inertia.
If a gun is falling, so is its trigger. The slide comes to an abrupt stop when it impacts a hard object, but everything else in and on the gun wants to keep moving. All those parts are stopped by the parts they’re connected to which are stopped by the parts they’re connected to. On and on until the part in question is the slide hard against the solid object.
The trigger, however, is out there dangling in space. It’s designed to move independently. Unsurprisingly, when a gun is dropped and impacts an object at a certain orientation, the trigger’s inertia tries to keep it moving in the direction in which it has been intentionally designed to move. The specific amount of force exerted in that direction depends on a handful of variables such as the mass of the object, its velocity, and the duration of its acceleration when it impacts the solid object (how quickly it stops).
In the case of the P320, the trigger shoe has enough inertia that, when the P320 impacts a hard surface at a sufficient velocity and oriented in such a manner that the force is relatively in-line with the trigger pull direction, the trigger moves.
Sure, there is an impact velocity at which the trigger shoe’s inertia would overcome the entire 5.5 to 7.5 pound trigger pull weight and actually release the striker. But this is not what’s happening in the P320 drop test discharges that we’ve seen. Overcoming that amount of resistance over the full pull distance is a tall task, indeed.
The Problem
What’s happening in the P320 is a confluence of two separate occurrences:
• The impact moves the trigger shoe rearwards through its pre-travel pivot. What may feel basically like slack or play in the trigger actually serves an important mechanical function: it moves the striker block safety out of the way. The trigger is telling the gun, “Okay, the trigger is being pulled on purpose, so clear the plunger out of the way of the striker so it’s free to travel far enough to impact the primer.”
• The impact jars the internal components, tests the limits of the fit between chassis and slide, and the striker slips off the sear. Only because the striker plunger was also moved out of the way by the trigger’s limited-but-sufficient amount of travel does the striker fire forwards unimpeded and ignite the primer.
We know this happens, because in both TTAG’s and SIG SAUER’s testing there were drop test incidents in which the striker released from the sear, but the gun didn’t fire. In those cases, the trigger hadn’t moved far enough (or soon enough) to clear the striker block. High-speed video (and reasonable postulation) showed other instances where the trigger moved far enough to clear the striker block but the striker did not slip off of the sear, and therefore the P320 also did not fire.
Both occurrences must happen together, with the plunger moving out of the way before the striker attempts to move through that space, for the gun to discharge.
The Fix
As we posted earlier, SIG announced a voluntary upgrade program for P320 owners. The Army’s M17 pistols, which came out of the Modular Handgun System trials, already have these upgrades and SIG reiterated that they were always planning to roll them out in the commercial P320s soon as well.
While this may sound like marketing spin, SIG has a reputation for regularly releasing generational product improvements (often to the ire of customers when “version 2” upgrades are not backwards-compatible). They also have a culture of continuous improvement. They never actually said “kaizen,” but the Japanese influence we’ve seen in their production philosophy was very obvious.
Additionally, from a purely economical standpoint it’s typically more efficient to produce a single version of a product than multiple versions. As much parity as possible across commercial, military, law enforcement, and other P320 variants makes sense. If all of the chassis and fire control systems, etc., can be the same, that saves production costs and increases affordability.
Production on current P320 models has been halted. The upgrades made for the MHS version of the P320 (the M17) are coming soon to the commercial P320 via the voluntary upgrade program. Those upgrades include:
A reduced-mass trigger shoe. The current version, which may change slightly before hitting the commercial market, is skinnier and significantly more hollowed-out on the back side. It also has a hole in the top rear. Mass is reduced by 34%.
This is, by far, the most critical upgrade component as it relates to drop safety.
A reduced-mass striker (a 25% reduction) and sear (a 37% reduction).
A trigger disconnect safety, which disengages the trigger bar if the slide is out of battery. This lever is seen at the top left of the chassis in the photo above (looks not unlike a sock puppet).
The sear housing geometry has also been changed.
SIG can and will perform all of these upgrades on current P320s if the owner so chooses. No change to the firearm’s serial number is necessary.
The Why
Based on feedback from users, including LE/Mil, SIG sought to eliminate the “double click” feeling of the trigger pull. Changes to the striker, sear cage, and trigger were done to facilitate this.
Some contracts demanded a trigger disconnect that disengaged the trigger completely should the slide not be fully in battery. So a disconnect was added.
In SIG’s quest for continuous improvement, they also lightened components wherever possible.
The Result
SIG brought us into their testing facility today and demonstrated that three upgraded P320s were all functional and fired properly. They then proceeded to repeatedly drop each one onto concrete at that precise -30° problem angle from four feet. At least nine drops in, none had discharged. That’s saying something considering TTAG’s redneck test resulted in two discharges in three drops.
Additionally, SIG showed us high-speed footage of both the current commercial P320 version and the upgraded trigger version impacting the concrete. The difference was night and day. While significant trigger travel was clearly visible on the current model, nothing but a quiver was visible on the new version.
Furthermore, we dropped off our P320 — the one we had tested — for upgrade work. As soon as the final version of the upgraded trigger is ready, SIG will be installing it and the other upgrades in TTAG’s gun and shipping it back to us. You’d better believe it’s going to meet concrete as soon as it’s back in Austin.
On Monday we’ll find out the details of how SIG is going to handle this upgrade program and what the logistics will look like for current owners. Stay tuned.