Thank you all very much for your replies. I want to go on record and say this is why I used the term "behavior" versus "defect" I see lots of people screaming defect when a majority of the time the issue is with the nut behind the gun.
The slide release reply makes perfect sense. She just had finished shooting the Glock and the magazine does not slide as easy as it does with the M&P. She does slap the magazine in on the Glock. I bet she did this on the M&P the first time as well. The magazine on the M&P just floats in with no effort compared to the G21.. And it never happened to me.
I also bet you are on to something with the grip and bumping/riding on the slide release. Again, it was the first time shooting the M&P. The Glock, which we've shot since 1995, with the double stacked .45 is much wider that the M&P. I bet we were both choking up on the grip being so used to the G21.
Guess we will just have suffer
and be forced to go to the range some more and work on the grip and magazine insertion techniques.
New question, should I be concerned about the 4-5 dry fires? These are my first .22's and everything I read has me terrified of dry fires and pin damage.
Thank you again for all of your comments.