Had a nice day at the gravel pit today, all to myself, and it was a sweet way to spend a day off.

Near the end of my shooting time with my EDC M&P9C, I noticed the magazines had ceased to drop freely. Since I own two of of them (one is none...) I switched to my alternate, which worked just fine. It seems the follower was riding up the tab attached to the slide release mechanism.
Getting home, I did the usual web research, which for some horrid reason, had folks modifying the magazine followers. This bothered me because one gun worked just fine, while the other one didn't, which is clearly state the fault lies in the gun, and not of the magazines.
So I stared at things, poked at various things with my calipers, and observed the subtle movements of the different parts to find the culprit. Having two guns to compare was key. There's nothing wrong with the magazines. It's a subtle manufacturing defect, and based on what I know about the process to make these parts, it's likely common in all M&P's that have this part. It's only a matter of time before it appears on your gun, primarily as a function of slight wear of the parts.

If you look carefully at the slide release, you'll note that it's all one single piece of sheet metal, beautifully shaped into a complex little component. Each end of the slide release yoke consists of a more or less U shaped bend, coming off the main yoke, then wrapping around and down over a cutout/partial slot in each side of the polymer body of the gun. If you were to push inwards (not up) on the right slide release, you'll detect a little bit of movement in that direction, but if you do the same on the left side, you'll find no play. This exists on both of my handguns, despite the stamping being slightly different between them in this area. Perhaps S&W realized where the problem lay and was attempting to correct it. The inside of the "button" drags slightly against the cutout, preventing inward movement like the other side. This is where the problem lies. The magazine follower pushes up against the tab on the left yoke arm, and there's about .02" difference in the location of the tab on the malfunctioning gun, where the tab is too far to the left, preventing it from resting properly on the follower shelf. Being that much closer to the edge of the cliff, it simply slides off too easily. A design with insufficient tolerance for manufacturing variations and wear, if you ask me.

Now that I understand the problem, the challenge is to find a way to get the tab to move over to the right a little more. This will be scary for some, but follow along. First, I needed the the left side of the yoke to move to the right, and I did that by lifting up the release lever and shoving a screwdriver (my worn out one on my Swiss Army knife was perfect) into the inside of the U bend. With a twist and a prayer, I opened the bend. Keep in mind this part is hardened after bending at the factory, so its not for the faint of heart or ham-fisted. The left side of the yoke was left jammed up out of it's notch, so I had to coax it back into place. Now, there's a gap on the inside of the bend, allowing some inward movement, just like on the right side. Next I need to bend the yoke (and thus the tab) on that side inward, to duplicate the gap between the yoke and gun body on the right side. I jammed the yoke on the left side back up, and then with some more careful prying inward between the inside of the body and the yoke arm (behind the tab,) crossing my fingers and saying a prayer, managed to get things bent the way I wanted just a little. I un-jammed the end of yoke back again, and checked for even movement on both sides. It's now back to no movement laterally, meaning it drags in the pocket, which means if the left side of the yoke and tab has been moved over slightly. It's a little bit sticky and stiff, but since it's metal rubbing against plastic, and I actually use the release instead of yanking the slide, it should smooth out soon enough.

Grabbing each of a handful of empty magazines, they all work just fine again. No hacking of magazine followers, either, which is fixing a symptom, not the problem. If you look at the aft end of the yoke arm on the left side, behind the slide release button, you'll see another small tab that's not on the right side. Previously, there was no gap between the end of the tab and the outside edge of it's pocket, whereas now there's a small gap, which is about the amount of movement I needed to get the tab to engage properly.

I hope this explanation made sense. It's hard to follow unless you have your eyes and fingers on the gun, and it would have been impossible to find without having a backup gun for comparison purposes.

Comments?