How old are the P99 mags?
Back in the early 2000's there was a revision to the 12-rd .40 mag butt plates due to similar breakage that occurred in some LE guns, mostly when the mags were being dropped onto hard surfaces (like concrete).
Of course, hitting the bottom of a duty weapon's grip frame against hard objects, especially carried in an exposed holster, has resulted in damage to mag butt/floor plates over the years, as well.
As I recall, Walther had Mec-Gar change the butt plate of the 99 series hi-cap mags to make it more resistant to that sort of impact damage. (The 10-rd butt plates are already pretty thick.)
This sort of thing isn't exactly unknown among firearm manufacturers who make LE/Gov service pistols, though, and other manufacturers have experienced it upon occasion. I remember when some LE Sig shooters were having breakage issues with old style mag butt plates, when they were being dropped during training/quals, for example.
I haven't experienced that sort of damage while training, practicing & qualifying with either my issued SW9940 (when I carried one for a few years) or my personally-owned SW99's, but then the agency range I typically use has a soft sand surface. I was lucky when using some outside agency outdoor ranges for field training, as most of the range surfaces were grass or soft dirt, but there were also a few with concrete and gravel surfaces. Those are hard on mags and their butt/floor plates.
Sub Club #9; .40 S&W Club #1953; S&W Club #3913
Retired LE - firearms instructor/armorer
Last edited by fastbolt; 01-31-2013 at 12:08..