Went to the range the other day and had an issue with my ten round mags. With fully loaded mags, about 3 or 4 rounds into the mag and the end cap on the mag broke. after the 3rd mag I stopped and looked at the pieces. All 3 broke in the same place, at the lip where the plastic end cap mounts to the metal body of the mag. Where they all broke at the same spot it made me believe it was a weak spot in the design. I have never had this issue with the 12 round mags, the trouble spot looks a little more beefed up than on the 10 round mags. So the next day I called the good folks at S&W and explained my issue. I guess this is a common problem because the guy I talked to new exactly what I was talking about. All my mags are the Mecgar ones and all were fairly new. Well I got to give props to S&W CS, They sent me out 4 brand new 12 round mags and when they get new end caps for the 10 round mags they will send me replacements for my broken 10 rounders. Just wanted to know if anyone else had this issue?

Yeah, I read in another forum that some guy had the same problem.  Seems to only occur in the .40 cal, 10 round mags though.  The 12 round mags don't seem to have any problems.

MecGar is factory supplier to alot of different brands of weapons....including S&W and Walthers...that said it is not their fault...
Walther makes the floor plates themself.... and yes it is only in .40 S&W 10 rounders that this happens
there is yet a easy fix to it... ask for S&W99 .40S&W floorplates
S&W CS rocks .... and cudos for them sending the 12 rounders....
there has been many people complaining about this issue... and apparently Walther fixed the problem...

I had the exact same thing JUST happen to me.  I emailed Walther and they are sending me replacements.  It's a known defect.