The description of the Walther P99 a couple of issues back in the Sitrep was accurate for the P99 DA, it was not true for the P99QA.
The QA (Quick Action), also called the anti-stress trigger places the pistol's striker in a pre-armed position. However, when the trigger is pulled, the striker has to move rearward to its point of release before it can travel forward and provoke a discharge.
The typical distance the trigger has to travel is about 8mm with a trigger pressure of 8.5 lbs. The button mounted on the top of the slide (left rear) is only a dismantling feature. It neutralizes the striker to allow dismantling the pistol without having to pull the trigger (like the Glock). Depressing this button on a P99QA will require the shooter to rack the slide to re-arm his/her pistol and will unnecessarily penalize him/her. The P99QA can safely be returned to the holster after chambering a round, as safely as you can holster a Glock with a round chambered.