Way back in 2007 or so, I bought a S&W M&P fullsize in .40 S&W.  Not the very first model, but a few revisions in.

A few weekends ago at the range, this happened:



Immediate symptom was that the slide failed to lock open on an empty magazine.  Then I noticed the slide looked weird and was angled up slightly.  Then I noticed...well, crap. :(

Contacted S&W that week, got a prepaid shipping label, got the ex-gun shipped in last Tuesday, receipt confirmed last Friday.  No news yet on what's to be done, but it's only Monday.

I long ago gave up trying to keep track of how many rounds went through what.  But this particular M&P has probably fired somewhere around 10000 rounds.  I've shot the piss out of it from day one because it is just so nice to shoot and so reliable.  

I replaced the recoil spring & guide rod unit at least once in the past 10 years, and am on my second set of magazine springs.  A few months ago, I had to swap out the slide stop, because the left side broke off.

I've shot nothing but PMC and Speer Gold Dot .40 S&W, plus the occasional box of some other factory ammo, for the last 4 years or so.  I can't say for sure when the slide started breaking, but when it finished breaking I was shooting Speer Gold Dot .40 S&W, 180 gr.

I would be happy if S&W just replaced the slide.  This particular M&P had a really nice smooth trigger.  Probably that's due to much use, but if I recall right it was pretty good from the factory.  I never felt any modifications were needed.

Have any S&W armorers or users seen this kind of failure?  Is there a known cause?

When Todd Green was torture-testing his M&P 9mm a few years back his pistol developed the exact same kind of failure in the exact same spot.

M&P slide failure

I don't recall, though, if S&W ever gave a reason for the slide cracking like that.

Is the rail peeling away from the slide at the front of the slide release notch?

Is that what I'm looking at?

Yup basically.

Uncanny, I had precisely the same failure as in the 9mm version mentioned above.

Must be a weak spot that was engineered out of later versions of the pistol.

I wonder if there is something about the slide release, a point on it, that is focusing all the energy on a small section of the slide. Over lots of time and rounds, especially when the recoil spring gets tired, it peels the edge.

Seems that way, doesn't it?  Looks like a stress concentration must have occurred, on the inside corner of the slide rail, right at the cut where the slide release stops the slide on an empty magazine.  But does that front edge of the cut (where it's peeled in the photo) ever even hit anything?  I don't have the pistol in front of me, but I would think that the slide would rest upon the slide release at the back of that cut, upon locking open.

The left side of my slide release broke off a few months ago.  So maybe it was getting hit rather violently by the cut in the slide.  If I recall correctly, only the left side of the slide release actually sticks up and holds the slide back, so I guess it makes sense that side of the release would break first.

I had a very informative conversation with some New Mexico state police yesterday,* on this topic and others.  They were motorcycle unit guys.  All but one carried the S&W M&P in .40 S&W.  The third carried a personally-purchased S&W M&P in .357 Sig.  He knew the round count within a few hundred, and said he keeps a close eye on the slide for the beginnings of any cracking.

I had heard that the NMSP started out with .357 Sig some years ago.  According to the sergeant, they actually started with .357 Sig Glocks (not sure which model - likely the Model 32?).  Those broke slide rails in a manner similar to what's been seen in the M&P.  I forget the round count, but the endurance of the Glock was deemed unsatisfactory.  So NMSP switched to the M&P in .357 Sig.  Same problem as with the Glock.  So those .357 Sig M&Ps were also withdrawn from service, and now they have the .40 S&W M&P.

I wonder if this slide-breakage problem was addressed with the M&P 2.0?  I haven't read up on all the changes, but doubtless there have been some.

I hope this slide breakage doesn't happen with my Shield.  Since it's a newer design, perhaps S&W has been able to find & fix the source of the problem.

*side note: it's sometimes nice to talk to cops in an informal, low-stress setting (this was at a motorcycle rally where they were providing escort for a charity event).  I didn't want to take up too much of their time with chitchat, but handshakes were exchanged and thanks given.

further note: they carry Speer Gold Dots.  Which is exactly what I carry.  You can't always go by the policy of a large organization, but I think ammo choice is one you're pretty safe in extending to personal use.

Mine's roughly the same age so I'm going to keep a close eye on that area.

10,000 rounds is not all that much, let us know how S&W handles this.

Good luck.

Lifetime Warranty. ..........

That's what I'm thinking. It's easy to rack up 2500-3500 rounds in a year especially with ammo prices these days. S&W will totally replace the slide as that is the only thing they can do to remedy the problem. I'll be changing my recoil spring on my M&P40c every year or 3500 rounds whichever is first. I have since switched to CZ's for my every day carry duties and sold all my M&P guns n' gear sans my M&P40c. It was/is such a soft shooting... concealable and oh so reliable pistol that I just couldn't bear to part with it even though it sits in the safe 99% of the time. I'll be keeping an eye on it closer in the slide area from now on!

Have not received anything yet. I contacted S&W a few days ago, and they?said they're going about 4-6 weeks on repairs. My pistol parts have been with them a bit under a month, so I'll just forget about it for another couple of weeks and be pleasantly surprised one day.

I'd be very surprised if they didn't replace the slide with no cost to you. Curious if they have addressed this. I would think they have.

Good news, everyone!

I got my pistol back today through FedEx with a brand new slide. They even remembered to move over the night sights. Which I had completely forgotten about.

I believe they left the original Barrel in there which is fine since it wasn't broken. I think only the slide itself and the parts attached to it are brand new.

It might actually be time for some new night sights. The ones on there are around 11 or 12 years old.

It may be a problem similar to the rear frame rail that occasionally broke off in some Glocks from the early 2000's, they determined that some rails were made with a machine that cut a sharp inner corner under the rail instead of a small radius, cracking started in that sharp corner and continued until the rail piece broke off.

If it was the whole rail all the through the slide I would agree with you but it almost looks like splitting a log with a wedge in the OP's pics. Strange, whatever caused it.

One year "warranty"; followed by a  " lifetime service policy" under which they still repair their guns for free.

.40 S&W breaks guns. Always has.

Have you noticed if the new slide is different in the affected area? Can anyone confirm if the latest iteration has a better design?