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My guess (and is it only a guess because I have not seen the slide first hand) is that the frame rail pushing down on the lip in the slide is that caused that failure. It looks like the the edge of the slide is pushed down toward the frame. It makes sense that the lip would fail there because it is not continuous because of the cutout for the slide release. It would be interesting to look at the crack under a microscope to see if it failed due to fatigue or if it was a catastrophic failure. Although because of the thin cross section it may be hard to tell.
 

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I do have access to one. My jewelers loupe could be helpful as well. We will have to work something out.
 

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Yes, of course it contacts the rear of the notch but did you actually read what I said? It's just a theory but I don't see any other possible part that could impact the front of the notch.


Yes I did, it's why I commented upon "no apparent battering" and continued about needing high speed video of the slide cycling. Just because something breaks doesn't mean it was caused by physical impact. There's a whole lot more failures due to unanticipated stresses.
 

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Todd,



Wondering what you have planned for the pistol now?



New slide and continue using the pistol frame?



Paper weight?



Has Smith and Wesson even indicated a new slide would be an option?



Thanks G
 

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Discussion Starter #247
Gunarr -- Smith offered to send me a complete new gun, so I'm sure if I asked for a new slide they'd give me one.



As far as we're all concerned, the test is over. The only thing left, which I'll do post-SHOT, is fire 25 more rounds to do a final accuracy test on the gun. I'm very interested to see how much (or if) the crack in the slide degrades the accuracy of the gun at 25yd. Since my accuracy testing ammo is 124gr +p HST, it will also give me a chance to take before & after pictures of the crack to see if another mag and a half of +p ammo did anything detrimental.



The gun, as-is, is now back in my possession. Smith will have it on display at the SHOT Show in Orlando next month. After that, it's mine forever. I'll keep it as a memento of the test. I'm toying with the idea of offering it to the NRA Museum for a year so they can display it, if they're so inclined.
 

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Todd,



Could you apply some white or red paint to the front of the slide stop lever and rack the slide as far as back as possible and see whether the front of the slide stop touches the front edge of the notch cut in the slide? If it touches you should see the paint on the slide notch. In mine, there is just less than 1mm of gap between the slide stop and the front of the notch.



After the last round is fired, the slide recoils and COULD travel far back so that front edge contacts the slide stop. May be this is one reason why Glock made a ramp instead of a vertical cut in its pistols. Glock slide cut



Since you have fired about 62K rounds, that is about 3600 batterings enough to create a crack. But then, your slide stop should also have broken. Did you replace that too?
 

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Gunarr -- Smith offered to send me a complete new gun, so I'm sure if I asked for a new slide they'd give me one.



As far as we're all concerned, the test is over. The only thing left, which I'll do post-SHOT, is fire 25 more rounds to do a final accuracy test on the gun. I'm very interested to see how much (or if) the crack in the slide degrades the accuracy of the gun at 25yd. Since my accuracy testing ammo is 124gr +p HST, it will also give me a chance to take before & after pictures of the crack to see if another mag and a half of +p ammo did anything detrimental.



The gun, as-is, is now back in my possession. Smith will have it on display at the SHOT Show in Orlando next month. After that, it's mine forever. I'll keep it as a memento of the test. I'm toying with the idea of offering it to the NRA Museum for a year so they can display it, if they're so inclined.


Thanks Todd,



Good to know, If I ever have a slide problem, I can contact Smith, get a new slide and move on with the psitol.



G
 

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Could you apply some white or red paint to the front of the slide stop lever and rack the slide as far as back as possible and see whether the front of the slide stop touches the front edge of the notch cut in the slide? If it touches you should see the paint on the slide notch. In mine, there is just less than 1mm of gap between the slide stop and the front of the notch.



After the last round is fired, the slide recoils and COULD travel far back so that front edge contacts the slide stop. May be this is one reason why Glock made a ramp instead of a vertical cut in its pistols.


I compared the clearance between the forward edge of the slide stop notch and the slide stop itself on the M&P, a 5906 and a Browning High Power (BHP). All had a clearance of about 0.030 inches or slightly less than 1 mm. The vertical displacement between slide stop and notch is about the same in all cases. The number of rounds in the magazine has no effect whatever on slide travel. Unless the frame material of the M&P flexes signficiantly, there is little chance that the slide stop and the forward edge of the slide stop notch will contact each other.
 

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The number of rounds in the magazine has no effect whatever on slide travel. Unless the frame material of the M&P flexes signficiantly, there is little chance that the slide stop and the forward edge of the slide stop notch will contact each other.


I think you misunderstood me. What I said was since the potential for the slide stop to contact the notch happens only after the last round is fired and since Todd has fired around 62K, it is around 62*1000/17(mag. capacity) ~ 3600 times the slide has been locked after firing a magazine fully.
 

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There is a possibility that the slide stop on Todd's M&P is slightly longer due to manufacturing differences. I found that the Sigma also has got the ramp like the Glock. Could someone explain the rationale behind the ramp if not for the reason I mentioned?


The avoidance of sharp corners reduces the incidence of stress cracks in the metal. Dunno at this point in time if this is an issue in this case.



I think you misunderstood me. What I said was since the potential for the slide stop to contact the notch happens only after the last round is fired and since Todd has fired around 62K, it is around 62*1000/17(mag. capacity) ~ 3600 times the slide has been locked after firing a magazine fully.


The slide stop contacts the REAR of the notch in normal operation, not the front portion where the crack developed. I flat don't believe that the acceptable manufacturing tolerances of the slide stop are sufficient to cause contact with the slide. This is especially true since the clearance between slide stop notch and slide stop are within generally accepted practices, which is what allows for tolerance variations.



I'm not sure what your concept of manufacturing tolerances are, but unless there are design specific specifications, there are commonly accepted standards. In either case, there will be a nominal size for the slide stop tab that engages the slide and a specified undersize-say 0.005 inches -that would be acceptable.
 

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The avoidance of sharp corners reduces the incidence of stress cracks in the metal. Dunno at this point in time if this is an issue in this case.







The slide stop contacts the REAR of the notch in normal operation, not the front portion where the crack developed.


I think you missed my point. After the last round is fired and the slide is recoiling backwards and the slide stop clears the notch, the slide stop raises up due to the magazine follower. At this MOMENT, the FRONT edge of the slide stops contacts(VERY CLOSE) the FRONT edge of the notch.



CLEAR THE GUN. Pull the slide backwards SLOWLY until it stops MOVING. DON'T RELEASE IT. You would find that FRONT edge of the notch and the FRONT edge of the slide stop ALMOST touch each other. I hope that gives you a picture of what I am saying.
 

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I think you missed my point.


No I haven't. You've overlooked my comment some posts back that the forward edge of the slide stop notch in the sample slide has no apparent signs of battering, which would be produced by your theory. More to the point: neither does the slide stop, which would show severe battering/wear from acting as the recoil shoulder for the slide. Moving parts around by hand does not give you an accurate representation of what ocurrs during the firing cycle. This is why I suggested high speed video as a possible means of determining what the takedown latch does during the firing cycle.



Troubleshooting of mechanical parts breakage generally involves a lot of blood, sweat, tears, toil, money and sophisicated equipment. In an earlier era, John Browning described it as "One drop of inspiration in a barrel of persperation".



While we wait for S&W to address the issue, you're free to butcher your slide stop as you will to alleviate your concern.
 

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Taking a hard look a thte pistol and location of the crack I noticed several items. First in the fully in battery position the left front slide rail as viewed from the rear actully extends well into the slide stop cut out notch. When the gun is fired the frame flexes. This can be seen in the glock and is called peening. Do a search on glock peening and you will see what I mean. I believe looking at the evidence at hand what is occuring is that the locking block is flexed fairly hard at firing. This is imparting a twisiting motion although minute that is leveraging the top front of the left front guide lug against the top of track in the slide and prying the bottom of the guide lug against the back of the track in the slide. This overtime causes the slide stop cut weakend part of the track in the slide to fail. It has zip point zip to do with the slide stop its self. The fix is to move the frame mounted tab on the left side farther forward so that it is not resting astride the slide stop cut at firing. Or ideally to shorten both the slide rail tab and the slide stop notch to provide better support to that portion rail at firing.



Just my .02, but the only logical explanation I can see.
 

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Taking a hard look a thte pistol and location of the crack I noticed several items. First in the fully in battery position the left front slide rail as viewed from the rear actully extends well into the slide stop cut out notch. When the gun is fired the frame flexes. This can be seen in the glock and is called peening. Do a search on glock peening and you will see what I mean. I believe looking at the evidence at hand what is occuring is that the locking block is flexed fairly hard at firing. This is imparting a twisiting motion although minute that is leveraging the top front of the left front guide lug against the top of track in the slide and prying the bottom of the guide lug against the back of the track in the slide. This overtime causes the slide stop cut weakend part of the track in the slide to fail. It has zip point zip to do with the slide stop its self. The fix is to move the frame mounted tab on the left side farther forward so that it is not resting astride the slide stop cut at firing. Or ideally to shorten both the slide rail tab and the slide stop notch to provide better support to that portion rail at firing.



Just my .02, but the only logical explanation I can see.


In retrospect a better fix would be to extend the left front rail tab on the locking block such that it fully extends back through the slide stop cut out notch and reengauges deeply into into the slide rail past the slide stop cut out. This would be simple miodification of the locking block only. It would affect no other function and would prevent any repeats of this issue. It would also be a simple and cheap retro fit for older guns. I would do extend the rail tabs on both sides of the locking block, just to over engineer the gun myself.



***Hey Smith if your listening I deserve a sample of each of the models so improved.****



Thanks.
 

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Fixguns, I'm right there with ya as to a cause for the failure. I havn't actually checked this thread in a few weeks, but did get into a discussion on the failure on another board. Came here to post a link to it and found that you came to the same conclusion I did.



Here's the link with some crappy pics I took this evening that show what you are talking about, as well as clearance between the slide stop and forward edge of the slide stop notch for the naysayers. If you read the descriptions for the pics, I actuallly pulled the guiderod and recoil spring to get the slide as far to the rear as possible before taking pics. Then I tried it without the barrel as well just for grins. At no time will the slide stop contact the forward edge of the notch, not gonna happen.



What will happen is the slide moving up and down with recoil and the guide rails stop the upward movement as the slide rises back into battery, and since the forward left side is only partially supported due to the slide stop notch, its a weak point.



Enough babbleing, here's the link.



http://www.ar15.com/forums/topic.html?b=5&...9945&page=4



So, if they fix it can I have a sample of the improved version as well?
 

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you guys don't think moving the guide forward or lengthening the guide on the locking block will result in weakening the block guide (tab) leading to it breaking at an even lower round count than a slide splitting? i'm not sure i would consider this split rail a defect or even an engineering problem. its more entropy than error or flaw, something is bound to give under a high rate of use or neglect and todd didn't really baby the gun. if it were a design flaw or something wrong with engineering then you'd see it occurring under "normal" usage and there isn't a track-record of split slide rails on the m&p under normal usage.
 

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Fixguns, I'm right there with ya as to a cause for the failure. I havn't actually checked this thread in a few weeks, but did get into a discussion on the failure on another board. Came here to post a link to it and found that you came to the same conclusion I did.



Here's the link with some crappy pics I took this evening that show what you are talking about, as well as clearance between the slide stop and forward edge of the slide stop notch for the naysayers. If you read the descriptions for the pics, I actuallly pulled the guiderod and recoil spring to get the slide as far to the rear as possible before taking pics. Then I tried it without the barrel as well just for grins. At no time will the slide stop contact the forward edge of the notch, not gonna happen.



What will happen is the slide moving up and down with recoil and the guide rails stop the upward movement as the slide rises back into battery, and since the forward left side is only partially supported due to the slide stop notch, its a weak point.



Enough babbleing, here's the link.



http://www.ar15.com/forums/topic.html?b=5&...9945&page=4



So, if they fix it can I have a sample of the improved version as well? :humbsup:


If yours and Fixgun's theory is correct, probably the left rail of the locking block should have broken instead of the crack in the slide as the locking block and sear assy are both MIM parts while the slide is forged. MIM is weaker than forged/cast parts as its density is at most 98% of normal steel.



I hope Todd will post something here once he hears back from S&W.
 

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If yours and Fixgun's theory is correct, probably the left rail of the locking block should have broken instead of the crack in the slide as the locking block and sear assy are both MIM parts while the slide is forged. MIM is weaker than forged/cast parts as its density is at most 98% of normal steel.



I hope Todd will post something here once he hears back from S&W.


Maybe I'm confusing terminology, but what exactly are you referring to as the "locking block"? From what I can see of the movement of the slide, the stress applied to the fracture area is where the stainless steel chassis is molded into the poly frame, not back at the sear assembley. Slide moves forward untill barrel ramps up locking tight in the slide, slide makes upward movement untill limited by the lug on the chassis. Maybe I'm calling it the wrong term, or have to dig deeper to see where the movement stops at, I stopped looking when I found movement that matched the direction of fracture.
 
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