Why did my optic shear off?

[Xmark1]

Yesterday, while shooting my S&W M&P 2.0 4.6 in barreled 10MM, My Holosun optic flew off and hit me in the face.
The two attachments screws/bolts just sheared off - see attached pictures.
I was shooting 180 grain projo's at 1,250 FPS.
I used the plastic adaptor plate that came with the pistol at time of purchase.
I also used the screws provided by S&W.
the screws were torqued to proper spec with blue Loctite.

Is there anyone that has knowledge or experience as to why this happened?

I can only imagine the joy involved in getting the broken studs out of my slide.

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[Koda]

My guess, either overtorqued (ruled out) or bad screw metalurgy.
I dont like the idea of a plastic adapter plate.... could that affect torque or cause some motion?

 

[spookshack]

I'd contact S&W 1st, as you stated you were using their screws and torqued to spec with locktite. Lots of folks on the internet who dislike/hate optic polymer optic plates. I prefer direct mount just to eliminate a possible failure point (less things to go wrong).

 

[Xmark1]

My guess, either overtorqued (ruled out) or bad screw metalurgy.
I dont like the idea of a plastic adapter plate.... could that affect torque or cause some motion?

I too, suspected the plastic adaptor plate.
A 10mm power load, IMHO, might make a plastic plate flex. It was about my 50th shot when this happened. Enough to rock them high carbon steel screws, and snap them?

 

[Koda]

I too, suspected the plastic adaptor plate.
A 10mm power load, IMHO, might make a plastic plate flex. It was about my 50th shot when this happened. Enough to rock them high carbon steel screws, and snap them?

Yes...

Im no engineer but I do work with plastics occasionally... it will have some level of flex or compression depending on type. I dont have your parts in hand to truly have an opinion but im surprised S&W used plastic if its an adapter plate.

 

[Xmark1]

I'd contact S&W 1st, as you stated you were using their screws and torqued to spec with locktite. Lots of folks on the internet who dislike/hate optic polymer optic plates. I prefer direct mount just to eliminate a possible failure point (less things to go wrong).

I think you are on to something, when direct mount is possible.

I just miked out the holes on my smith as well as an extra Vortex Defender I have, and it would be a direct mount to what appears to be larger screw holes in the slide.

I have used the same kind of Holosun optic with a metal adaptor plate on my G17 with great success, thousands of rounds. But the 9mm is a lot less violent.

 

[spookshack]

My 1.0 CORE came with steel plates. I believe S&W switched to polymer with the 2.0 CORE. There is a S&W forum called MP-Pistol.com. The OP could poke around over there for info.

MP-Pistol Forum

A forum community dedicated to Smith & Wesson M&P Pistol owners and enthusiasts. Come join the discussion about optics, performance, gunsmithing, troubleshooting, reviews, accessories, classifieds, and more!

www.mp-pistol.com

 

[Nosferatu]

Get one of these: https://chpws.com/product/sw-core-2-0-1-975/

 

[Xmark1]

Yes...

Im no engineer but I do work with plastics occasionally... it will have some level of flex or compression depending on type. I dont have your parts in hand to truly have an opinion but im surprised S&W used plastic if its an adapter plate.

When I bought the pistol about10 months ago, it came with many plastic adaptor plates. And I figured S&W know what they are doing - Perhaps as far as the plastic plates, they were wrong.
I love the ergonomics of this pistol, and it is a real tack driver. I already sent a few thousand rounds downrange with iron sights and have had no issues.

 

[spookshack]

It would seem the gun industry is moving away from steel plates to polymer plates. Several top name brand guns come with them now.

 

[Xmark1]

Get one of these: https://chpws.com/product/sw-core-2-0-1-975/

Good Looking Out!

I use those same adaptor plates on many other pistols.
They are also aesthetically pleasing. See the pic I posted of one on my G17.

 

[Deavis]

Are you using the optic as a charging handle for the slide?

 

[Xmark1]

It would seem the gun industry is moving away from steel plates to polymer plates. Several top name brand guns come with them now.

Like most businesses.
Cutting expenses and lowering quality.
Learn from my calamity folks, it appears as if you would be wise not to use polymer adaptor plates.

The world I was born into no longer exists.

 

[Xmark1]

Are you using the optic as a charging handle for the slide?

No. I never do that, it would make the glass dirty.

 

[Xmark1]

Yes...

Im no engineer but I do work with plastics occasionally... it will have some level of flex or compression depending on type. I dont have your parts in hand to truly have an opinion but im surprised S&W used plastic if its an adapter plate.

Pictures don't lie. Here is a photo of some of the adaptor plates that came with the pistol. Plastic!

 

[Kruel J]

Pictures don't lie. Here is a photo of some of the adaptor plates that came with the pistol. Plastic!


View attachment 1980587

The plastic may have enough give to it that the optic could "vibrate" ever so slightly with recoil. Enough vibration and screws fail, especially tiny optic screws.

 

[Certaindeaf]

It sounds like your wrists aren't limp enough.

 

[Koda]

Pictures don't lie. Here is a photo of some of the adaptor plates that came with the pistol. Plastic!


View attachment 1980587

Again, I dont have your parts in hand but my Trijicons mount with two posts milled in the slide (metal) to prevent inertia.
Now if an adapter plate is needed, and its made from plastic... i just dont see how the plastic posts would prevent inertia movement, thus shearing the mounting screws.

 

[arrowshooter]

I suppose this could be a result of two items of dissimilar composition not playing nice together. Like aluminum heads and iron exhaust manifolds. Gunna break a screw or two just because.

 

[Xmark1]

Again, I dont have your parts in hand but my Trijicons mount with two posts milled in the slide (metal) to prevent inertia.
Now if an adapter plate is needed, and its made from plastic... i just dont see how the plastic posts would prevent inertia movement, thus shearing the mounting screws.

I suspect there would be angular momentum compression on the plastic.
Perhaps as the gun is fired and the slide moves back - the optic rocks forward ever so slightly, as the plastic compresses. The screws being the fulcrum point.
And when the slide bottoms out wide open, the momentum of the optic may compress the rear of the plastic mount in the other direction?
Do this enough times and high carbon steel will break because it is "strong" not "tough". And, of course, tough steel would break also given enough rounds fired.

Just speculation at this time, but I am a mechanical engineer.

As far as using a slide milled for a particular optic, that is a double-edged sord. Two of my slides were milled to accept a certain optic only and they work well. But the rub comes when you think about how many footprints are out there. The slides I had milled for Doctor/Noblex now hold optics that have been discontinued. This is a problem if I wanted to change to say, an RMR footprint.