MEC-GAR +2 ADAPTER (NOT SHIPPED TO RESTRICTED STATES) F42099-SET
[F42099-SET +2 POLYMER BASE MAGS]

Works fine with zero problems or hiccups in my S&W original M&P 40C 10 round mags. Takes them to 12 round with no problems thus far. And you can believe this or not...it's real...I actually get 13 in one of the two mags (that's 13 inside one of the 10 round mags). I ordered these to test out after seeing the comments and pictures on the S&W forum (older posting) when someone posted a question looking for a possible +2 option for the original 40C (10 round mags). Put one in the chamber and ran 13 in the mag for a total = 14 and had no problem with this true compact running them & cycling them through lickidy split...now that's FMJ's as I just got these yesterday (6-15-'19) and all I've done so far is spit out FMJ .40's....will test out HP's later (it's Fathers Day so I'm busy). But needless to say I was quite surprised that one magazine took 13 rounds....your mileage might vary. You will need to do some sanding on the front lip of the +2 extension to cut the sharp lip or your ring finger "WILL" let you know when it's time to stop. So I did that and the difference is night and day. There is a discussion on the Smith & Wesson forum concerning this and how the poster went about doing it. I suggest you follow his lead and just do it. You won't regret it. But the point of the matter of all this "blah-blah" here is that this +2 mag base, that is NOT designed nor marketed for any S&W/M&P mag, DOES WORK just fine for both the .40 cal's and 9mm short original Compact magazines for those of you guys and gals looking to up your round count on-board.....So, there ya go.