Odd Slide Lock Back Issue - M&P 1.0

[Jellybean]

Maybe a derp question, but here goes;
Was helping a friend out with some gun stuff;
They have an M&P 1.0 Fullsize in .40S&W.

I noticed an odd issue where, when pulling the slide to the rear manually, it does not always lock back reliably with a magazine inserted. I would pull the slide back expecting it to lock, and it would go forward as if there was no mag inserted. However, with certain magazines inserted, it would lock back as intended.

Of course I immediately suspected a mag issue, or maybe even a worn slide release/worn release spring.

However, when firing, it locks back normally on an empty mag as it should, and IIRC does not seem to care which mag is in the gun. And this is even with weak Tula ammo.

Now, I KNOW it isn't one of us accidentally pressing the slide release, since we both had the same issues with the same mags when attempting to lock it back on an empty mag manually, and it still locked back fine when firing.

So I'm kind of stumped. I still want to say it's a mag issue, but... what do you all think?

[dwhitehorne]

I'm guessing dirty mag first then maybe a weak spring. When you manually pull the slide back the spring pressure alone has to push the follower up to catch the slide stop. When firing the last round the jolt from the slide violently cycling could be enough for the follower to overcome any dirt/debris and correctly slide up the magazine body. The weak mag spring would usually cause the follower work properly when cycling manually but not when firing. That's why I'm wondering if the mags in question are just dirty especially since it is a 1.0. When is the last time the mags were disassembled and the inside of the mag bodies and followers wiped down? David

[Jellybean]

I'm guessing dirty mag first then maybe a weak spring. ... When is the last time the mags were disassembled and the inside of the mag bodies and followers wiped down? David
That's a good question.
I'm guessing probably never.
Will have to follow up on that.

[mpom]

Maybe this will apply, maybe not: in the 9mm version there was a change in the design of the follower, as sometimes, with wear, the follower would not engage the slide lock. Newer followers fixed this issue, by having a larger "pad" that pushes up on slide lock. Worth checking into this.
Mark

[Hadoken]

Maybe this will apply, maybe not: in the 9mm version there was a change in the design of the follower, as sometimes, with wear, the follower would not engage the slide lock. Newer followers fixed this issue, by having a larger "pad" that pushes up on slide lock. Worth checking into this.
Mark
I had a 9mm M&P that if the magazine release was swapped to the right side (for a lefty) the follower would catch on the magazine release hole in the mag and stop the follower from rising up. Happened with all 3 of the magazines I had and immediately soured me on the platform. Any chance his release is on the right side? You probably wouldn’t notice the issue without cycling snap caps or rounds though since you would see the follower stuck down in the mag body before you inserted the mag.

There’s a thread over on Brian Enos with multiple people having the same problem and S&W denying it. They just didn’t test out swapped the mag release it seems.