S&W M&P not returning to battery, cycles sluggishly

[the naked prophet]

My wife has a S&W M&P .40 that has been back to S&W for premature slide lock and failure to return to battery. They replaced the slide lock spring with the newer, stronger spring, and that's fixed. They "modified" the barrel to solve the FTRTB problem.

However, when we tested it with about 100 rounds, it had one round that didn't chamber completely. The problem is that the slide returns mostly to battery, but gets stuck just far enough back that the barrel hasn't risen to the locked position. When the trigger is pulled, there's a click and a tiny little dimple is left on the very upper edge of the primer. If the round is put back in the mag, it always fires just fine, and if the slide is tapped forward instead of pulling the trigger, it fires just fine.

When shooting it myself, I noticed that the slide was cycling sluggishly, with kind of a ker-chunk feel. It moves back smoothly, but the forward motion has "a hitch in the get-along." None of our other autos do this.

Does anyone have a solution to this problem? It seems like the spring just isn't strong enough to push the slide forward hard enough to close all the way reliably. Either that or the barrel doesn't smoothly lock up with the slide, and that's stealing enough energy from the slide that it can't lock up.

Wolff doesn't make springs yet for the M&P, otherwise I'd just try that first. Any other ideas?

 

[RH45]

Is that with factory ammo, or reloads?
If it is with reloaded ammo, remove the barrel, and "chamber check" your ammo by dropping them in the barrel to see if they fit.
If that's not the problem, with the slide off, try sliding the ammo up, under the extracter. It's possible it's too tight.

 

[the naked prophet]

All factory ammo. I'll check the extractor when I get home.

 

[RH45]

Even with factory ammo, it might not be a bad idea to chamber check them. It is possible that the chamber is tight.

 

[berkbw]

BTW, all "factory ammo" is not created the same, eh? A lot of cheap ammo is really dirty, a lot of cheap ammo does not expand the case to seal the chamber.

I would:
Clean out the chamber to CLEAN and smooth;
Buy a box of "normal" ammo - Wal-Mart WWB is ok;
Shoot it and see.

If you still perceive a problem, take it to your dealer, he'll call S&W, they'll send a call tag, have it picked up, fixed, and returned.... NO charge.

If this IS a case of chamber reaming failure, it will be the 1st I've heard about from these guns. But then, there is always a 1st, eh?

b-

 

[the naked prophet]

The gun was impeccably clean. Even if it wasn't, it should still shoot fine. I had over 2000 rounds through my Glock before I cleaned it, and it had no malfunctions. I'm not going to carry (and won't let my wife carry) a gun that jams due to a little dirt.

The chamber did not have any burrs or rough spots.

If you still perceive a problem, take it to your dealer, he'll call S&W, they'll send a call tag, have it picked up, fixed, and returned.... NO charge.

Been there, done that, just got it back.

We have been using a variety of factory ammo: Winchester white box from wal-mart, Remington green box from wal-mart, Remington golden sabre, Federal HST and Tactical Premium, etc.

 

[the naked prophet]

Forgot to mention: I checked the extractor, and it's quite sharp and has a burr! It is quite difficult to get the cartridge up under the extractor. I'm going to pull it out and see if I can smooth out the burr just a bit.

 

[the naked prophet]

Update: I sanded down the rough spots on the extractor, and it's noticeable smoother, but still wouldn't return to battery while loading a cartridge unless the slide had pretty good momentum. It seems that the spring power is virtually nil when the slide is almost closed.

So I found a Glock "recoil buffer" that I had sitting around (got a bunch for free - see no use for them myself) and trimmed it down so it fit on the M&P. Now it's basically a 1/16" disk that fits in front of the recoil spring. It adds enough oomph to the spring that it chambers fine now, but still allows the slide to cycle far enough back to engage the slide stop. I'll test it out tomorrow morning and report back.

 

[RH45]

I think I read something in this thread about being able to use Glock recoil springs
http://www.brianenos.com/forums/index.php?showtopic=30124

Otherwise, maybe you can find some information on the M&P website.
http://mp-pistol.com/boards/portal.php

 

[the naked prophet]

I tested it out. Out of a hundred and something rounds, not a single malfunction except when my coat sleeve (hey, it's 17 degrees here) got stuck in the slide.

The slide still cycled... chunkily? It was sluggish, and make a ker-chunk noise when cycling, but it cycled. I tried my best to limpwrist it, and couldn't get it to not go into battery. I'll shoot some more, and have her shoot it some more, but if things keep going this way, I'll say it's ready to be carried.

 

[RH45]

Maybe it was just that your extracter had a burr on it.

I would hope that if you shoot the snot out of it that it will smooth out.

We beat you, it made it all the way up to 19 degrees up here

Good luck!!!

 

[loop]

What would concern me is that the gun was not in battery and the firing pin left a mark on the primer.

If it had detonated you would have had a serious problem.

I would have started with polishing the feed ramp, chamber and rails.

I would have sent it back with an out-of-battery primer indent.

 

[Coronach]

What type of ammo are you using? What bullet profile? If you check the link in my sigline, the problem you describe exactly replicates what happens when I use "truncated cone" bullets in my M&P. My gun will feed flat-nose bullets perfectly, but will choke on truncated cone almost every time. The two look very similar, but are different enough to induce failures, with the TC bullet having sharper angles.

Mike

 

[the naked prophet]

What would concern me is that the gun was not in battery and the firing pin left a mark on the primer.

If it had detonated you would have had a serious problem.

I would have started with polishing the feed ramp, chamber and rails.

I would have sent it back with an out-of-battery primer indent.

The primer dent is uniformly tiny and shallow. Less than you see when you chamber a round and then eject it from an AR or AK. I don't think it's an issue, it appears that the firing pin block is working fine.




As far as the ammo, it's mostly the winchester white box which I would call the truncated cone. However, even the flat tip rounded shape of the Federal HST has the same problem. We can't find any other ammo with less than a truncated cone shape.

 

[Coronach]

As far as the ammo, it's mostly the winchester white box which I would call the truncated cone. However, even the flat tip rounded shape of the Federal HST has the same problem. We can't find any other ammo with less than a truncated cone shape.

Hmm. While my gun will not feed TC ammo, it will feed HST flawlessly. So...not quite the same problem, or a more serious version of it.

Contact S&W and let them know it's still not running right.

Mike

 

[skinewmexico]

What are you using for lube?

 

[another okie]

Disassemble the gun and remove the barrel.
Drop each round you plan to shoot into the chamber and see if it slides in and then drops out relatively easily. If they all do, the ammo is not the problem.

 

[the naked prophet]

For lube, I'm using an NLGI #0 aluminum/moly grease on the slide rails, and Hoppes Elite on everything else. Minimal lube, but enough to keep it slick. For what it's worth, my Glock will run with absolutely zero lube...

All of the ammo will drop into the chamber just fine, smoothly, with almost enough room to rattle around in the chamber. S&W said they "modified" the barrel, and all I can tell they did is polish the chamber.