Sunday, November 06, 2011

M&P Function Experiment

So here's the M&P experiment to see if its just mine that does this or if it is something that I shouldn't worry about much.

1. Make sure the M&P is empty
2. Feed a dummy round into the chamber
3. Pull the slide back partially.  On the slide, scale #2 from the end sits over the rear pin.  Pull the slide back so scale 3 sits over the pin hole
4. release.

Does your slide go back into battery or does it do this?

The slide does not go back into battery and the recoil spring guide protrudes from the front. Slide can be pushed forward into battery and there's a thunk as the barrel goes back into position.

Repeat the experiment by going to scale 4 and the same thing happens.

I think this may be a symptom of the functioning problems I was having with the gun as when it locked up it was not fully in battery and gave only light primer strikes or no primer strikes at all. Then again, this may be normal as it just went through 100 rounds without a problem.

I suspect the recoil spring is not strong enough to pull the slide back into battery, leading to failures once enough rounds are fired and the gun gets dirty. In contrast, my Glock 17 will promptly close when pulled back a similar distance.

So if you've got an M&P9 and want to do this test and tell me your results, I'd appreciate it.


God, Gals, Guns, Grub said...

Have you thought about just doing an inexpensive swap of a new spring in case the spring is just a weak one...

Just curious...

I don't own and M&P, but my good friend has two... the 9mm and 45ACP... the 9mm has thousands of round through it... no problems...

Dann in Ohio

Keads said...

I just completed your experiment on mine. Its had 400 rds through it without cleaning. It went back into battery.

Hope that helps!

JD Rush said...

+1 to what Keads said. I just ran 300 through mine without cleaning, and it closed fine, horizontal or vertical. If I dry fire, scale 3 does not reset the striker, scale 4 does. Try flipping your takedown lever down, carefully put the dummy into the chamber (I did it without losing a fingernail and without snapping the extractor over the cartidge rim) and repeating the test. I think mine feels like it is harder to move the slide this way, but I have no strain gauge to measure the difference. How free is your striker? Does it bind?

Aaron said...

Yep, I suspect it is the recoil spring and will be doing a swap. I'm puzzled as it ran without any issues for over 2000 rounds and now this.

It is even more strange considering it is right back from factory repair and you'd think they would have diagnosed and replaced it or otherwise let me know.

Of course, they may have totally misunderstood the problem. I had described the problem in detail before getting an RMA and then again sent a detailed explanation of the fail to fire along with the pistol.

When it came back, the service receipt with it said "customer complaint was rough trigger" and that it was fixed. I assumed there wasn't a code for "it doesn't shoot on occasion when trigger is depressed", so they slotted that in as the repair code. They did replace the trigger return spring as it was a different color upon return, but not the recoil spring.

ZR: I tried your test and it seemed to have the same effect as before, with no real difference.

Off to buy a new recoil spring and we'll see what goes.

Scott said...

If the spring doesn't work, maybe there's an edge somewhere that needs a little relief with appropriate abrasives? If the barrel hood on an M&P locks into the slide at the ejection port (like your Glock or my XD) that would be the first place I would look. Could also be on the cam.