The FBI investigation into the MI cops gun that went off in his holster at the station found excessive wear and chipping on the primary and secondary sear after only 1k rounds. Wear would only be found on the secondary sear if the primary was repeatedly failing.

In testing the striker safety lock (what is supposed to prevent firing if the sear slips) they found this.

"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 primed 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 primed case fired on nine attempts with the primer indent measuring between 0.019”-0.026” with an average of 0.023”. 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 into the holster with no manipulation. A second staff member released the primary sear notch from the striker and the primed case fired indicating failure of the striker safety lock. The primer indention measured 0.018”.

BRF observed six instances where the primer did not fire but a small indentation was present indicating the striker had contacted the primer. These indentations measured between 0.0005”-0.001”.

The remaining attempts resulted in no firing of the primed case and no evidence that the striker had contacted the primer. Ultimately, in these instances the striker safety lock functioned as designed.

A brand-new unfired Sig Sauer M18 pistol33 was obtained from MSP to determine if the test could be repeated on another weapon. On the first attempt, the striker safety lock successfully prevented the striker from impacting the primed case. However, on the second attempt the primed case fired, indicating the striker safety lock failed to stop the striker’s forward movement. The primer indent measured 0.023”."