Opinions and theory on the Sig P320 drop failures and UCDs
Disclaimer: This is all informational and for educational purposes only. Only modify your firearm if you are an experienced gunsmith and at your own risk.
Where to start with the ongoing saga of the P320?
The Sig Sauer P320 was a cutting-edge design when it was released, offering consumers the ability to interchange grip modules for an unparalleled level of pistol customization.
Interestingly, this innovative design didn’t originate as the P320. It was first introduced as the P250 platform — Sig's original modular pistol. The major difference between the two platforms is that the P250 was a hammer-fired, double-action-only (DAO) pistol. Rather than designing the P320 from the ground up, Sig modified and upgraded the P250 platform into a striker-fired system. Many believe this foundational decision may be at the root of some of the platform’s ongoing issues.
In contrast, the P365 — another modular pistol from Sig — was designed from scratch. Although it uses the same modular concept, its smaller size and more modern engineering make it a favorite among the concealed carry crowd.
Numerous 2A-focused content creators — such as LFD Research, "Three P320s in a Trench Coat," and Wyoming Gun Project — have conducted in-depth analyses of the P320’s troubling history with drop failures and uncommanded discharges (UCDs).
Sig’s initial response to the P320’s drop failures in 2017 was to launch a voluntary upgrade program. This included a thinner curved trigger and a sear redesign that added a redundant safety feature.
SIG Sauer P320 Manual Safety: Oversight or Opportunism?
Sig also introduced a manual safety kit priced at $100 — though customers were still responsible for paying a gunsmith to modify their Fire Control Unit (FCU) and grip module to install the components.
What bothers me about this manual safety is that it functions merely as a trigger interrupt, not as a true sear block like the manual safety on a 1911. If Sig’s goal was to offer a trigger-disabling safety, a much simpler and more cost-effective solution would have been to implement a split-trigger system — similar to those used by Glock, Smith & Wesson, and others. A split trigger would have only required replacing a single component and would not have necessitated any FCU modification.
Instead, the manual safety retrofit involves replacing or adding four separate parts and altering the FCU chassis to accept the safety lever — significantly increasing labor, cost, and complexity. Was this simply a misstep in design? Possibly. But to me, it feels more like a cash grab than a consumer-focused safety upgrade.
For a company attempting to rebuild trust after a high-profile safety failure, Sig’s approach here feels less like thoughtful engineering and more like monetizing a crisis. A simpler fix was available — they just didn’t take it.
Fast forward eight years — the gun community has developed several solid theories explaining why these uncommanded discharges (UCDs) have occurred.
When Sig offered its voluntary upgrade program, one of the key changes was replacing the original sear with an updated version. This new sear design added an additional safety feature, aiming to address concerns over unintended discharges. See the comparison below:
Sig added a protruding leg to the post-upgrade sear, clearly visible on the right side of the image. The intended function of this leg was to provide pressure against the striker disconnect lever and prevent the sear from disengaging unintentionally — a safeguard to address drop-induced discharges.
However, this change introduced an unexpected and controversial side effect: the upgraded sear now actively interacts with the trigger and trigger bar during its motion. Specifically, when the sear is depressed, it actuates the trigger mechanism and lifts the striker safety disconnector — effectively defeating a key internal safety feature.
Why would a safety “fix” introduce new behavior that compromises an existing passive safety mechanism? That’s a question many in the firearms community continue to ask.
As I mentioned earlier, the P365 was designed from the ground up unlike the P320, which was adapted from the older P250 platform. Interestingly, despite the P365 sharing a similar modular fire control unit (FCU) concept, it has no reported history of drop failures or un-commanded discharges.
Even more surprising, when I looked up the P365’s sear, it strongly resembles the pre-upgrade P320 sear — the very version Sig replaced in response to safety concerns. This raises a legitimate question: if the original P320 sear design was so problematic, why does its apparent twin function just fine in the P365?
In my opinion, Sig never fully understood what was causing the P320's uncommanded discharge issues. Their response — the voluntary upgrade program — felt more like throwing fixes at the wall and hoping one would stick. Yet even after the rollout of these so-called upgrades, the problems persist.
Just a few months ago, a new potential failure point came to light: the P320 takedown bar. Specifically, the takedown bar from the P320 9mm/.40 S&W/.357 SIG models is not interchangeable with the one from the .45 ACP/10mm models, despite looking nearly identical. The size difference is small — easily missed by the average user — but significant enough to create serious issues.
Mixing up these parts can put the disconnector lever and magazine stop out of spec. Here’s what proper reassembly should look like:
- Lock the slide back using the slide lock.
- Rotate the takedown bar.
- Release the slide lock.
- Let the slide go forward.
At this point, you should be able to insert a magazine — because the magazine stop has disengaged correctly.
But what happens if someone reassembles the pistol incorrectly, say, the way you might a Glock? You simply pull the slide back slightly, rotate the takedown bar into place, and then release the slide. If the slide lock was never engaged, the trigger bar doesn’t properly disconnect the sear. With a post-upgrade sear, this results in the striker hook catching on a partially engaged sear — a dangerous condition that leaves the pistol in a precarious state.
To make matters worse, the post-upgrade sear doesn't drop fully in this scenario. Instead, it leaves a small lip — just enough for the striker hook to catch. This wouldn’t happen with a modified post-upgrade sear, where the leg is trimmed off; in that case, the sear drops completely, and the striker hook has nothing to catch on.
One emerging fix in the gun community is to physically modify the post-upgrade sear by removing the added leg. According to a recent video from Wyoming Gun Project, this modification appears to eliminate the striker engagement issue during improper reassembly. Their footage clearly shows that when rotating the takedown bar into disassembly mode, the sear ramp fails to drop fully — leaving the lip that creates the engagement risk.
While this DIY fix is absolutely not endorsed by Sig, it presents some damning evidence: the very safety “upgrade” that Sig implemented may be introducing new failure points under certain conditions.
Closing thoughts
I hope this breakdown has provided some useful insight into the ongoing issues surrounding the P320 platform. While some may view this as overly critical of Sig, the company’s handling of these concerns has been far from exemplary and raises legitimate questions.
Allegations have surfaced suggesting that Sig has held private meetings at their headquarters with social media influencers — many of whom, after previously voicing skepticism or criticism, have since changed their stance and now publicly support the company. This alone raises eyebrows regarding transparency and public accountability.
Even more concerning is the recent passage of a law in New Hampshire — Sig’s home state — which effectively shields the company from liability in civil lawsuits brought by individuals claiming that a flawed P320 design caused bodily harm. The timing and implications of this law cannot be ignored and further fuel the perception that Sig is more focused on legal insulation than on addressing consumer safety.
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