Had my first malf of any kind with the M&P 9 at the range on Sunday.
Loading rounds into a mag while conversing with Shootin' Buddy and one of the ROs, I noticed the top round got really hard to depress and glanced down to see that the only witness hole on the side of the mag facing me that was not showing brass was #17. "Oh," thinks I, "It's just almost full," and bear down as hard as I can (as in "put my back into it,") to squeeze the round in.
#17 was still empty. I flipped the mag over and see that brass is showing in #16, so I go to stuff another cartridge in there. No dice. The rounds won't budge.
Whatever. I threw the mag in the pile with the other loaded ones and commenced to shooting.
In the middle of one string of fire, the slide stops out of battery. Examining the mag showed the top round nosedived in the magazine, having been jammed forward by the slide hard enough to set the bullet of the Speer Lawman round (not noted for having anything you'd call a "crimp") halfway back into the case.
Pulling it out of the mag allowed the remaining rounds to rattle around loose in the mag tube. Bwuh?
I tipped the mag upside down and shook it, and the remaining rounds clattered out onto the range table. A look at the mag showed that a corner of the follower had hung up in the cutout for the mag catch, halting its upward progress at a sever tilt, which had presented the rear rim of the top cartridge to the oncoming breechface while the nose of the round was still pointed down into the mag tube.
Weird. Best I can tell, the follower somehow got canted as I was loading it. I used a paint marker to add a little "sad face" next to the number on the mag floorplate and I guess I'll be buying another M&P 9 mag the next time I'm in a gun store. As long as it never does it again, I'll continue using it at the range, but one more foul-up out of it and it's going in the trash after getting pounded flat so that nobody fishes it out of a trash can and potentially winds up getting themselves killed trying to save a couple bucks.
Not to sound like a broken record, but magazines are wear items. Replace as necessary. Do not get married to your magazines.