I wrote the following on AR15.com-
I ordered a factory M&P 9mm barrel for the fullsize from Brownell's this week. It came today. My plan was to see if it was dimnsionally the same as the 40 S&W, since the 9 and 40 M&P fullsizes are, essentially the same guns.

I took some measurements and some side by side photos-











The 9mm barrel locked up nice and tight, It was not loose or ill fitting in any way. I had called S&W and asked a tech guy about the dimensions of the 9mm and 40 slides. He said that dimensionally they are the same. Of course he went on to tell me that I should buy a dedicated 9mm and not use a different barrel...then he said quietly, wink, wink.

Then I broke out the digital calipers-

40 S&W barrel-




9mm barrel-




Next was a function test. Using the new barrel, my M&P40, some Tula 9mm from Wal-Mart and a 40 S&W mag-I have a 9mm mag on order from 44mag.com, it's just not here yet-I went to test it in my unofficial test range out back.

It functioned flawlessly, with one exception-right before the last round, the follower would engage the slide stop, not feeding the last round. That is due to the mags being for the larger diameter 40 round. The smaller 9mm round allowed the notch in the follower to hit the slide lock before chambering the last round.

I expect that to be solved with a factory 9mm mag. I would have had a magazine had any of the local shops had one in stock yesterday, when I was in town.

I will test it again when the new mag arrives.

Here is the schematic to the M&P from Brownell's-
Schematic for Smith & Wesson® MP (Semi-Auto) - World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools

As you can see, the 9/40/357 guns share the common parts, with the exception of the barrels. 40/357 has it's mag and 9mm has it's mag.

UPDATE 101/03/2011-

Went to the range today for a test. I traveled to Louisville, KY to shoot at the an door range-Welcome to Bluegrass Indoor Range located at 4402 Kiln Court Louisville, KY 40218 (502) 451-9088. Great bunch of guys there and the prices are affordable.

I took 200 rounds of 115gr 9mm. 150 of it was Tula, not know for being all that clean and 50 rounds of Federal Champion.



Distance was 21 feet. Course of fire was slow, double taps and rapid-as fast as the range rules allowed.

No failures to feed or eject, one failure to fire and I blame that on a hard primer-it was the Tula ammo. There was a noticeable dent from the firing pin. I reset the sear and it did fire the second time.

The Tula was nasty..very dirty. The Federal Champion had a huge fireball. The Tula did not.

All and all, I'm happy with the test and now have 2 guns in one.

Not being a gunsmith and also being fairly new to the auto pistol I have what may sound like a stupid question. Could you in fact put a 40cal barrel in a 9mm slide or would the difference in the locking lugs cause a problem? It doesn't seem to have caused a problem going from 40cal to 9mm.

Sorry if that doesn't make sense.

Dave

Can you start with either pistol and buy the other barrel?

Ha! Someone else asked the same question...

I know from experience that a 357Sig barrel will work straight away in a 40 or visa-versa. I'm pretty sure a 9mm barrel will work in a 357 M&P with the 9mm Magazine and possibly a 9mm recoil spring. Bob

The problem is breachface,with the smaller calibers,and the extractor tension holding the casing against the breechface and in the right spot, same can be done with glock,BUT you can experience FTF and other issues occasionally, Ive never done it but others have ,Im sure S/W doesnt approve and I dont have any idea if any serious problems can occur due to recoil etc,Nice if it works especially for target practice. Bob

Dave, I cannot attest to whether a 40 barrel will fit in a nine slide. I wish I could help.

Perhaps someone with both guns can chime in and try it.

Thanks. I think it is probably too much to hope for. I know Glock people have told me it doesn't work with a Glock.

Dave

I would really like to know if the 40 barrel will fit the 9mm slide. Who has both and can try? That would be too cool.

The rim of a 40 caliber round won't fit in the 9mm breechface.

KAC

Thanks KAC, that should have jumped out at me, but I guess I'm still learning. Pretty logical.

Dave

Excellent write up! I'm intending to buy a full size .40 as well & get a few .40/9 mags with a 9 barrel. My goal is to have the .40 for SD, 9 be target as I can just about always find 9, but less frequently on my .45 (for my .45c, cheaper to shoot 9!).

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Gen1 4513TSW
M&P 45c

Can anyone comment on what the differences are between a 9mm "conversion" barrel meant for the .40/.357 and this 9mm replacement barrel?

Dave, thanks for doing the T&E on the 9MM barrel. I plan on getting one for my M&P compact 40/357 Sig.

Not a problem..and it's Dan..

If you have the discount at Brownell's the barrel is $65...

Midway sell's them for $65, but they are on backorder.

I just - last week - put a 9C slide and barrel on top of a 40C frame, and the 40C slide and barrel on top of a 9C frame....

(Of course, I had all the necessary magazines.)

Worked fine.... Dimensions ought to be about exactly the same - or at least within tolerances. It appears that the guns are identical except for the breech face and the bore size.

The reason? The 9C came through with a thumb safety, and I'm a 1911 guy, so I decided that I wanted that on the 40C I carry around the house. I was a little concerned - the sear block on the 9C has a headed sear pin, and the ejector is a little different, but everything worked. I was prepared to swap sear blocks and figure out how to install the thumb safety in the one from the 40C, but it wasn't necessary.

(FWIW, I, too, find the thumb safety kind of silly on this gun, but I'm used to it, and I didn't want it on the 9C. That one's supposed to go to my daughter if she doesn't stay in New York.... My problem is that I think it'll turn itself ON on it's own, and if you're not used to it - there's really no need to leave it on - you've got a problem. Since I'm used to a thumb safety, no problem.)

One funny result. The 9C tended to toss empties up over my head, while the 40C sent them off to the right. Now they both seem to toss 'em over my head ....

Someday....

It appears that the .357Sig barrel is all you need for that conversion, btw. The magazines are compatible. Haven't tried it. (Can't think of a good reason, but that's another thread.)

The .45 versions are NOT the same sizes, AFAIK. I don't think you can put a Compact slide on a Full Size frame, either, although....

Regards,

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Stu.

I want to bump this back to the top to find out anything new on these 9mm conversions with oem barrels & ask if anyone else has tried this with the M&P 40 pro 5" barrel. Also would like to know what the reliability of the 9mm barrel in the 40s&w is turning out to be. I want a target pistol in 9mm that I can also use as a HD pistol in 357sig & 40s&w. If the 5" oem barrels swap the same way as the compacts seem to do then this is the answer. If not I will be buying the Glock 35 which has many conversion options awaiting me after purchasing it. I am totally intrigued with this 9mm OEM barrel conversion drop in concept.

I have a Sig 229 Sport in 40 S&W which I "converted" to an IDPA pistol using a Barsto 9mm Conversion barrel and an extra stainless slide. It functions perfectly using the 10 shot 40 S&W 229 Sport magazines with the extra metal finger extention.
I had a Dan Wesson 1911 in 40 S&W and tried using a 9mm barrel but the slight difference in breechface dimensions cuase feeding/extraction issues. I finally had another slide fitted by DW for use with the 9mm barrel.

I just tried this last Saturday after ordering a factory 9mmP barrel and spare mag from MidwayUSA. It worked like a champ. It would not feed more than 5 or 6 in a row from the .40 mag, but with the 9mm mag it functioned perfectly with FMJ ammo (I didn't have any jhp with me to try).

I bought a M&P 40 with a 5" barrel. When I went to the gunstore to buy it, I told them about this thread. They took out a M&P 9 with a 5" barrel and installed the barrel into a M&P 40 with same length slide. Every time they racked the slide back the barrel wedged itself into the slide and kept the slide from returning to battery. This happened at least 5 times & then they announced to me that it does not work.

I ended up spending $150 dollars on a Storm Lake conversion barrel because they told me that the 9mm 5" barrel didn't fit into the M&P 40 (5" barrel) at the store. They wouldn't let me try it myself because they said that I might break the gun & they would rather that they be held liable for any damages instead of me. Did I get lied to by the store employees in the hopes that I would buy a 9mm M&P from them instead of ordering a barrel on the internet? Is the 5" barrel so different from the 4" barrels that you can't swap out 5" barrels but you can swap out 4" barrels?

I guess I need to hear from some one who has swapped out 5" 9mm & 40s&w barrels with success...or failure. Anyway, the storm lake conversion barrel I bought has been perfect in my M&P 40. It shoots at least as accurate as the OEM barrel & I have not experienced any FTF's of any kind. So maybe I spent approximately $50-$100 more than I needed to, but at least it performs and isn't junk. But then again, blowing $100 in this great depression causes great depression. OK peoples, talk to me...

...Upon further reflection, I do know that I can't make my conversion barrel wedge itself in the slide like the 9mm barrel did at the store. There isn't that much play in the slide that would allow the barrel to travel within the slide like it did when the employees were trying it. There was something amiss in that experiment which allowed for that barrel to be able to travel back and wedge itself in the slide...

ET.:

It was my understanding (remember that this is the Internet and everybody's an expert) that it was considered better to use a Storm Lake barrel for this sort of conversion than the S&W barrel....

Apparently, there are differences between the slides that cause issues with the stock barrels....

I had no problems putting a .40 top (slide barrel & spring) on a 9mm frame, and vice versa (40C and 9C), but that's supposed to work - the rails & such are supposed to be 100%.

(Sounds nuts, but the 9C frame had a thumb safety that I preferred to be on the 40C and was too lazy to swap sear blocks and cut the frame for the thumb safety.... Way too silly to buy another Compact to do this, but I had 'em both anyway....)

Regards,

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Stu.

The benefit of an aftermarket conversion barrel like Storm Lake is that it is made to the dimensions of the factory .40 barrel, the only modification being the bore. You can see the obvious differences in the two factory barrels, and as always, YMMV. What works for one gun may not for another, there can always be minute variances.

My 40/9c has worked flawlessly with the Storm Lake barrel. To me, that assurance is well worth the little extra $$.

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Fast is fine;accurate is final

In order to prevent the slide from holding up on the magazine, could you change out the plastic magazine follower in your magazine to one that initially fits 9mm rounds? I am assuming the metal part of the magazine is made to the same dimensions for 9, 357, and 40 calibers.

Also, does anyone have pictures of what the gun looks like with a stainless barrel as apposed to the standard black finished barrel that comes stock from smith?

The feed lips on the .40/357 magazine are slightly farther apart than on the 9mm. (Just checked that today when I finally got hold of a .40 mag.) Whether that's enough to cause a potential problem feeding, I don't know.

I'd suggest using the correct mag for the caliber if at all possible. Yeah, I KNOW they're hard to find. I'm guessing the only reason the store I found one at today had a few 40s was that they'd jacked the price way up. They were out of the 9mm. (But at least I'll be able to shoot the 40 once I finish assembling the new slide and barrel.)
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Just did a quick check. I'd have to say DON'T try to run 9mm out of the .40 mag even with the 9mm follower. The 9mm rounds ride high and are barely retained, tilting upward at the front, which is also why the follower comes up so high with one round remaining. And if you try to put .40S&W in the 9mm mag, at least with what I have, the bullet case tends to catch on the front edge of the magazine.

Thanks Robotech. I was curious if that would work. Too bad it doesn't because swapping out the plastic magazine follower would be a $4 solution and not have your name on a 6 month waiting list!

Not sure if this has been completely answered. A .40 barrel will not lock up in a 9mm slide since the ejection port on the 9mm slide is actually smaller than that of the .40S&W slide. Some people have suggested you can trim some of the barrel hood off the .40 barrel to make it fit but you wouldn't be able to use it in a .40 slide. Also if you trim too much off then you just scrapped the barrel.

I had a few ejection problems while running a 9mm barrel in a .40 slide, which is why I don't recommend it for carry. I think it might have to do with the breach face and extractor tuning. I know a 9mm slide would alleviate the problem completely, but I also hear the "conversion" barrels do too simply because they actually slightly shift the location of the 9mm round higher into the breach face for a positive interaction with the extractor.

I believe u are over looking something here. A few members have successfully trimmed the .40 "tangs" down on their barrel to make it fit in the 9mm slide (of course this was with the Shield also). After those "tangs" are trimmed down, the .40 barrel is pretty much the same as the 9mm barrel. Which is why the .40 barrel then fits into the 9mm slide...........Now we also know the 9mm barrel drops into the .40 slide and works perfect. So since this .40 barrel is now the same size as the 9mm barrel. We also know it'll drop right back into the .40 slide. Of course the tangs on the .40 barrel are a very very tiny bit smaller than it was before. But it fits just fine and is basically like dropping a 9mm barrel into the .40 frame.............Once again, this is with the Shield. The FS could be a different weapon.

The barrel extension is indeed narrower on the 9c barrel than the 40c. It is visibly narrower, maybe .030 or .040 or so (I have not measured, but have observed the two side-by-side.) Others' experience indicates a 9mm barrel will work in the 40 slide, but one might expect some loss of accuracy as the rear of the barrel floats from side to side a few thousandths, and possibly unreliable ejection as the wider breech face may engage the 9mm case less securely. I have back ordered a S&W 9c barrel for my 40c from Midway for $65. I could try peening it or stippling it to widen the barrel extension, but that would not be without risk; if it shoots well, I will leave it as-is. I'll let you know how it goes, but it might take months to get it.

Hey I know this thread is old but did you use .40 mags in the 9c

I agree. Earlier this year KKM Precision built and sold to me their .40-to-.357Sig conversion barrel (4") for the M&P 2.0 and it works just fine.

I recently checked their website and discovered that KKM also makes and sells their .40-to-9mm conversion barrel for the M&P 2.0. Here's the link: M&P Compact 2.0 40S&W to 9MM (4.0″ Model) | KKM

Email from KKM confirms this is a drop-in barrel - no fitting needed. Just drop in the barrel and use 9mm magazines.

I'm buying one of the .40-to-9mm barrels so I'll have all three calibers covered with one chassis.

with the 9mm in a 357/40 slide conversion barrels, they typically offset everything .022" ish to the right on the barrel blank to properly bring the case head under the extractor hook. You wouldn't see this by eye most likely.

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NRA RSO