M&P 9C: Slide Goes Into Battery When Mag Is Loaded -- A Problem?

[Charlie Foxtrot]

My wife bought a S&W M&P 9C for CCW. Good on her! However, it may have a problem.

While reloading the pistol, about half the time the slide will slam forward when the mag is driven home with normal force. If the mag is slammed home, the slide will go into battery all the time. I'm no pistolero, But I've always thought that going into battery uncommanded was a failure, in need of fixing. She took it back to the Big Fish store, where their guru told her that all M&Ps were designed to do that. Just like Glocks... Wut??? My Glocks don't do that.

I asked her to talk to S&W Customer Service to see what they say. SWMBO is less than happy about having to do that. I need some expert advice to convince her, so I thought of this place. Unfortunately, we're in separate states while I renovate our old house for sale, so I can't handle it directly.

Thanks in advance.

[TR675]

Search the forum for "autoforward" and you'll find folks who think this is a feature and it's great, folks who think it's a bug created by Satan to torment us, and folks who are meh about it.

I'm pretty meh about it. M&P's do tend to autoforward more than other autopistol makes and models, but others will do it too - it's just not as frequent or easy. Best explanation I heard before I quit caring (take this with a grain of salt) was that the tool/backstrap pin that projects down to mag level gets bumped by your hand during reloads imparting KE to the frame, inertia on the slidestop will do the rest. Notably my full size will autoforward all day long but my compact - which has those pointy finger extension baseplates on its mags and thus does not have its mags slammed home hard - rarely if ever does.

I do not expect the pistol to autoforward; if it does, that's a nice bonus; if not, I hit the slide release and am ready to overhand the slide as a failsafe if the slide release isn't cooperating (I find it slippery and hard to engage, especially on the compact).

[BobM]

Most of the M&Ps in my experience do this (I own a few and my dept owns about 30). I'd rather they wouldn't since it's not 100%. My 5906 would do this but only after it had six or seven hundred rounds through it without cleaning.

[DocGKR]

I've had M&P's, Glocks, some 1911's, as well other pistols auto-forward. No big deal.

[LittleLebowski]

They were not designed to autoforward, however that does not mean there's anything wrong with the pistol.

[TheTrevor]

Small sample size, I know, but the M&P 9 full-size I borrowed at Rogers on Friday would auto-forward pretty much as reliably as my HKs when I reloaded with authority -- but on one occasion, which of COURSE happened during one stage on The Test, it failed to go completely into battery upon auto-forwarding. I'd never seen that before. (I got a re-shoot on that stage, but I had actually been doing better on the first run before the gun choked. Something about the Chief Instructor standing over your shoulder to up the psychological pressure a bit...)

[archangel]

I don't see autoforwarding as either a feature or a bug. It's just physics in action.

When you slam a mag in, the mag bottoming out and/or your hand hitting the bottom of the grip imparts some kinetic energy to the frame. Most of that is directed up, but due to the grip angle, some of it is also forward. So the frame will move a little bit, up and forward.

The slide is heavy, and because objects at rest tend to stay at rest, it lags behind as the frame moves. All it takes is the the slide retracting (actually, the frame moving forward) just enough for the friction between the slide and slide catch to be overcome by the slide catch spring, and the catch will drop free and allow the slide to go forward.

There are things that can be done to reduce the likelihood of autoforwarding, like changing spring weights, or the angle of engagement between the slide and catch. Some of those "fixes" could have potential negative impact on the pistol's function (like the recoil spring being to heavy to cycle, or the slide catch being so well engaged that it cannot be released by any method other than slingshot). But regardless of what you do to prevent autoforwarding, there will still be a force at which a mag slammed in will cause it to happen. Unless you have a 90 degree grip angle.


TLDR version: Autoforwarding happens because <science!>

[TheTrevor]

Excellent post, archangel. On other forums, that would be immediately promoted to a sticky at the top... 'round here, it's just another day on PF.

[JonInWA]

Great post, Archangel. My Gen 3 Glock G17 does it, as does my Ruger P89. Interestingly, both will do it only with a loaded magazine, so mass/weight/inertia is a causal factor (or perhaps the bullet of a loaded magazine making contact with the inner portion of the slide stop/release).

It's not a big deal to me, since whenever it's happened, the top cartridge has also been successfully chambered. I simply look at it as kind of a "reloading bonus."

Best, Jon

[Slavex]

recoil spring weights definitely affect how easily this happens (again science), all my Shadows do this much more easily with the 11lb recoil spring than they do with the factory one (13lb? can't recall right now). I do look at it as a feature, but learned the hard way to not expect it.