So I am getting ready to purchase my 3rd M&P
I own a gen 1 9mm
And a gen 2 .40 compact

The M&P is the only pistol I personally shoot.

.40 is my preferred caliber but I really like the idea of having a 4.6" barrel optics ready M&P 2.0 with 10mm capability for SHTF.

But .40 is what I know I will practice with. The Internet is crawling with answers. But I figured I would ask again has anyone had experience shooting .40 from their 10mm M&P? I know Glock 20 users can but I wondered how it has worked out for M&P users.

P S. I already know the warnings about headspace extractor wear - all that jazz. I just want to know if anyone has experienced reliability, feeding and or spring issues firing .40 from their 10mm?

I don’t know about the M&P, but I used to shoot .40s out of a 10mm 1076 all the time. No problems at all.

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Rule of law, not a man.

For my G-40 I just ordered a KKM .40 barrel for it. I didn't even have to change springs. It drops .40 brass 2 to 3 feet away, reliably. It makes for a very sweet 40 if not a CCW pistol.

Interesting, does the 40 not head space on the case mouth like a 45? Noob here, sorry for what is probably a silly question for most.

Would be better to have a 10mm barrel and a .40 barrel, also a magazine. You don’t want to use .40 in a 10mm barrel as the 40 will headspace on the extractor instead of the case mouth. And that will sooner or later break the extractor.

(As you noted) I once shot a whole box of .40 out of my Glock model 20. Functioned just fine. I wouldn't make a habit for the reasons noted but it does work.

It is also possible to shoot 9mm out of an M&P 40 compact barrel.

Don't ask me how I know this.

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What, me worry?

I tried a couple of magazines of .40 in my Glock 10mm, and it seemed to work fine. Not so much in my 10mm Colt Delta - wouldn't feed. I think a 10mm pistol with an extra .40 cal barrel is the smart way to go.

Larry

It does. The reason this can work is the extractor is strong enough to hold the cartridge against the breech face and withstand the firing pin blow. I guess you could say the .40 in a 10mm chamber is headspacing on the extractor.

^^^^^^^^
This, but a G29.

I agree with the using a 40 barrel, mags and recoil spring, especially if for SD.

That’s where the 610 shines
I have a Colt Delta Elite with 40 and 10mm BarSto barrels, Colt magazines and correct springs for each round, 18 and 24 pound respectively.

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213th FBINA

This is the answer. You are asking the extractor to be as strong as the barrel, so it is not a long term solution. Next figure out how easily parts will be available in an emergency, short or long term. Get a different barrel for a different cartridge.

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Front sight and squeeze

It is odd that the Colt wouldn't feed 40's. I have a p16-40 Para-Ordnance. It fed 40s perfect. Dropped in a 10mm barrel and it feeds 10mm perfect. Only difference in the barrels is the depth of the chamber cut. Used same mags and all. I did install a stronger recoil spring later. Friend of mine reamed his 40 barrel to 10mm depth and it fed fine. Maybe it had something to do with the non-ramped barrel of the Colt. Para is ramped.

Now that I think about it, maybe the 10mm spring was too strong for the 40 and it was short stroking?

Rosewood

As others have said, using the extractor to head space could eventually cause wear or breakage of the extractor. Not to mention, if the case ever gets past the extractor on chambering, it won't fire and you will have to dig out the round. A correct barrel is probably the best solution.

Rosewood

Thanks for all your answers everyone.

With this info I guess I will go with a 5" optics ready M&P 2.0 in 9mm then or a threaded barrel 9mm M&P

Those seems like a better fit for my needs.

Why not a 5" 40?

I have a 5" M&P 2.0 in 40S&W. I shoot it incredibly well. Think the long barrel really helps me to shoot it better.

Rosewood

Yeah, but they have the trajectory of a Red Rider BB gun. Don’t as me how I know!

Good to know. I didn't see any 5" optics ready .40 options on S&Ws website.
The cool thing about .40 is it can always be converted down to 9mm.
I have seen the 5" barrels in action and they work so well they look like they negate the need for compensators. Which has advantages.

Mine isn't optic ready. It does have the rail on it. I would assume they have one that is optic ready. May have to research that more.

Guess it is the 5" barrel, but I shoot it really well. Better than most other guns I own. Seems hard to miss with it.

Rosewood

S&W used to make a Ported version (both 1.0 and 2.0). Perhaps you may have seen these? Either way the greater weight does help muzzle flip.

I watched a guy do this at a USPSA match in OKC once. Really slow stage time because each round had to be cycled by hand. After the shooter finished, the holes in the targets were keyholed. Puzzled, I picked up one of the spent cases and the light bulb came on. The 9mm cases looked like they were ready to give birth to.22s.

There's always the Model 610 revolver. It's listed on the S&W website as both 10mm and 40 S&W. I have one and I love mine.

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Let's be careful out there

I've been shooting 40's out of my Glock 20sf and 29sf for over two years, my local gun store guy was a pro for awhile and stated he had over 10K rounds of 40 out of a 10mm Glock. I also have a 610-3.....

For my 1911's I just bought a .40 barrel and mags.

Logically, unless every single 10mm case was the exact chamber length for the rim to touch, it is not head spacing on it, the extractor is holding it...I am pretty confident that every 10mm case is not perfect in every 10mm chamber...

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Plastic has no soul

Yes, but u have to use moon clips for the 40s or else they are too deep for the hammer to strike. Moonclips are designed for that , they grip the rim what 3/4 of the way around, extractors only grab a few thousandth of an nch.

This true, but no chance of the round slipping past the extractor with a 10mm