M&P 2.0 CORE shearing screws

[Hill2933]

Recently bought an M&P 2.0 CORE in 9mm. After a few hundred rounds the optic launched itself downrange after both mounting screws sheared off. Sent it back to Smith and remounted the optic after receiving it back. After less than 100 rounds, one of the new screws also sheared off. I see multjple people posting about the same issue. Will a different mounting plate help with this? Should I have a gunsmith mount it to mke sure its not me? Or should i scrap the reddot idea all together? Still have to get the new broken screw removed.

 

[crosseyedshooter]

Which red dot, which screws and how much torque did you use?

 

[Saudade]

Which red dot, which screws and how much torque did you use?

What he said and which plate?

 

[SoCalDep]

Here’s the mounting procedure we use, and it’s been adopted by a lot of law enforcement agencies and training organizations:

• 1. Ensure you have all the correct parts. This includes optic, proper plate, sealing plate if necessary (Trijicon RMR), and proper/proper length screws.
• 2. Ensure the optic is functional.
• 3. Test fit everything to make sure the plate and screws fit, the plate/optic fits flush, and the screws don’t impede function.
• 4. Degrease all interacting parts. This includes the threaded holes in the slide, any threads in plates, and the screws themselves. I degrease the entire optic pocket as well so oil doesn’t migrate into areas where it could compromise the threadlocker.
• 5. Apply threadlocker. Loctite-248 is the best general-purpose threadlocker for most optic mounting situations. DO NOT use VC-3. It might work... maybe... if you apply it perfectly and allow it to air-cure for 30-45 minutes and don’t use too much. I’ve seen optics installed with VC-3 come loose over and over. I refuse to use it and even C&H has moved away from it. Loctite requires no air curing time because it cures in the absence of oxygen once installed.
• 6. Torque to the proper spec, which is generally the lowest of any interacting part. For example, if you’re installing a Leupold DeltaPoint Pro to an M&P with the S&W supplied screws you want to use the S&W spec of 15in/lbs, not the Leupold DPP spec of 25in/lbs.
• 7. Use an oil-based paint pen to apply some paint to a surface (I use the wrapper from one of the alcohol pads I use to degrease) and then use a sharp toothpick to apply indicator marks to the screws and optic body so that if it starts to come loose you can see and possibly deal with it before the screw shears.

We do not re-use screws if they come loose. The optic is remounted from start to finish with new screws.

We have pistol/optic combos with both the plastic and metal factory M&P plates as well as C&H with tens of thousands of rounds using this mounting method and no issues. When we do have problems (such as with old version C&H plates and the Holosun 509T on M&Ps) it usually turns out to be something other than the mounting method and we can usually get to the bottom of the problem.

 

[jschmidt]

Your problem is over torquing the screws. They should be about 15-18 inch pounds. You'll need to buy an inch pound torque wrench. Wheeler has a pretty good one

 

[SoCalDep]

Your problem is over torquing the screws. They should be about 15-18 inch pounds. You'll need to buy an inch pound torque wrench. Wheeler has a pretty good one

Or under-torquing, or lack of thread locker, or lack of degreasing, or failure to properly seat the components, or crappy screws, or the wrong screw or lots of things.

With the information given there is no one definitive cause.

I would prefer to identify the actual problem before throwing out guesses as to the cause. That’s why I posted our methods. I’d be interested in how the mounting in this case deviated from that. Then we can start to narrow down the major factors causing the failure.

Plus, torsional forces dissipate quickly after the application ceases. In my experience, over-torquing to the point of plastic deformation (beyond the yield strength of the material) is rare in 6-32 screws. I’ve seen it in 4-40s, but shearing is way more common when an optic comes loose compared to being “too tight”.

 

[jschmidt]

Or under-torquing, or lack of thread locker, or lack of degreasing, or failure to properly seat the components, or crappy screws, or the wrong screw or lots of things.

With the information given there is no one definitive cause.

I would prefer to identify the actual problem before throwing out guesses as to the cause. That’s why I posted our methods. I’d be interested in how the mounting in this case deviated from that. Then we can start to narrow down the major factors causing the failure.

Plus, torsional forces dissipate quickly after the application ceases. In my experience, over-torquing to the point of plastic deformation (beyond the yield strength of the material) is rare in 6-32 screws. I’ve seen it in 4-40s, but shearing is way more common when an optic comes loose compared to being “too tight”.

I'm comfortable with my diagnosis. He said "shearing" not coming loose.

 

[SoCalDep]

I'm comfortable with my diagnosis. He said "shearing" not coming loose.

Unlike stripping heads, screws most commonly shear after coming loose during firing. Again, torsional forces dissipate rapidly once the application of that force has stopped, so unless he torqued it down to the point that he literally shared it while he was torquing it down, it’s exceedingly more likely that it either wasn’t torqued down enough or that the thread locker didn’t do its job, resulting in the screws coming loose and ultimately sharing off.

The forces exerted upon screws once they are loose are extreme, and it doesn’t take much in terms of rounds or time for them to Shear.

I say this having personally mounted a few hundred pistol optics and watched around 750,000 to a million rounds go down range from pistol optics. Our team once put 1,985 rounds through an M&P with an SRO mounted in around 20 minutes. We sheared one of those screws and it was because it came loose, not from over torquing (we suspect the heat from firing that fast caused the threadlocker to give up, which resulted in one side coming loose first and ultimately shearing). The other side was almost there when we caught it.

I’m not trying to start an internet war, but given the description, saying over torquing is the cause is the gun equivalent of Web MD saying you have cancer because you have a headache.

 

[jschmidt]

I'm comfortable with my diagnosis.

 

[SoCalDep]

Ok. Good discussion. Thanks for your well reasoned and valuable input based on a logical argument, experience, and knowledge regarding the use of pistol optics and engineering behind fasteners and forces that act upon them. I’m sure the OP appreciates your input.

I’m so glad to participate in a forum with such an open exchange of information… where questions that are asked are answered by those who want to provide the most appropriate answer for the person asking rather than making themselves feel “comfortable”…where ideas are debated to further understanding, develop knowledge, and maybe improve our own understanding.

 

[Rick H.]

The only times I have seen a screw "shear" is when it came loose and the adjoining part became a cleaver and cut thru the screw. This can also happen if you over tighten a screw and stretch it thereby reducing it's ability to hold something. In any event I would look at how the screw(s) were initially installed and secured. Follow the advise of SoCalDep and you will be in good shape.

Rick H.

 

[dmike]

I recently had the same issue. the red dot hit me in the face while shooting and examining the issue I found both screws sheared off. I have sent it back to the factory to have the slide drilled and retaped. After sending the pistol back to S&W i found the type1 plated had 2 tabs on the forward end 1 was stripped. I have several M&P optic ready and this has never happened.