There was a change made to the .40 Auto magazines after initial P99s in this caliber experienced this problem of premature slide lock-back. The original magazines had orange followers. The redesigned magazines have a blue follower, along with an indent on the right side of the magazine body just below the magazine catch cutout that serves to keep the bullets away from the portion of the slide stop lever that engages the magazine follower. Walther America may replace your orange-follower magazines with the newer blue-follower magazines if you are experiencing this problem. See FAQ III-8 and FAQ III-9 for more details about the changes made to the .40 Auto P99 followers and magazine tubes.
For more recent P99s chambered in .40 Auto, or for P99s in general, the slide stop spring may be the culprit for this issue.Back to FAQ or Go to Next Question