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  #1  
Old 11-17-2013, 11:23 PM
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Default 40 to 9 Conversion

I know it's probably been asked before, so please forgive my inability to do the search. I'm lazy like that!

Can I use a S&W Factory 9mm barrel and 9mm mags in my M&P 40's slide without any issues? Or is there a big difference between the size/outside diameter of the 9mm barrel vs the 40?

I know Storm Lake makes their conversion barrels, but they're never in stock and kind of pricey. I would also like to stick with S&W parts if possible.

Thanks in advance, and feel free to beat me with a big stick for asking something that's probably very redundant.
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Old 11-17-2013, 11:26 PM
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Yes. and yes
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Old 11-18-2013, 08:20 AM
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Awesome. Thank you.
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Old 11-18-2013, 02:05 PM
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It's my understanding the M&P 40 was developed first and the M&P9 was built on the same frame. The difference being a 9 barrel and mag.
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Old 11-18-2013, 02:27 PM
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A couple of weeks ago I was talking to S&W customer service about another matter & asked him about ordering 9MM & &.357 SIG barrels for my 40C. He told me that they weren't taking orders for barrels at this time & didn't know when they would.

If you find that they are let me know. I'd just as soon have factory parts, too.
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Old 11-18-2013, 03:44 PM
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I bought my factory 9mm barrel from Midway USA. It cost about $65 at the time. They have been out of stock for months now though.

You may have to go with Storm Lake or KKM for now.
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Old 11-19-2013, 09:01 AM
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I'm wondering if the extra slop where the barrel hood mates with the slide reduces accuracy; specifically when you put a stock 9mm barrel into a 40 slide.

However, for $165, a KKM 9mm conversion is reasonable.

On a related note, I purchased a KKM 40 barrel for my new 40L, and am having the stock 40 barrel's hood thinned in order to fit my 9L CORE slide.
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Old 11-19-2013, 10:20 AM
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I purchased a factory barrel from Midway, and a 9mm mag. Everything dropped right in, and I have had no problems at all.
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Old 11-19-2013, 01:44 PM
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Quote:
Originally Posted by AwfAxis View Post
I'm wondering if the extra slop where the barrel hood mates with the slide reduces accuracy; specifically when you put a stock 9mm barrel into a 40 slide.
It absolutely will. The lock up between the slide and barrel is the critical component of accuracy. If the lock up is not tight, then it has the effect of the sights moving every time you shoot.

The M&P lock up is completely done at the chamber/slide interface. The barrel touches the slide at the muzzle, but that isn't the critical component of the lock up. Even so, the barrel should not move at all once the slide is forward.
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Old 11-19-2013, 01:56 PM
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Don't know that much about the 40 to 9 conversion, but thought that on the conversion kit that the 9mm barrel outside diameter was the same as the 40. The inside diameter is smaller. I think I saw it on YouTube.
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Old 11-19-2013, 02:03 PM
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What about the diameter of the shell in relation to the extractor and ejector? The 9mm shell is quite a bit smaller in diameter than the 40/375 Sig.
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Old 11-19-2013, 02:16 PM
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Quote:
Originally Posted by alde View Post
What about the diameter of the shell in relation to the extractor and ejector? The 9mm shell is quite a bit smaller in diameter than the 40/375 Sig.
Extractor and ejector are the same parts for 40/357 and 9.
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Old 11-19-2013, 02:19 PM
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Quote:
Originally Posted by alde View Post
What about the diameter of the shell in relation to the extractor and ejector? The 9mm shell is quite a bit smaller in diameter than the 40/375 Sig.
I thought this would be a problem as well. However, it seems that S&W uses the same breech face and extractor for the 9mm guns.

I just measured the external chamber dimensions of both 9mm and .40S&W factory barrels. They are identical. Therefore, the 9mm and .40 slides are the same as well. This is why the extractor doesn't need to be changed. It must just move out a little more when shooting .40S&W.
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Old 11-19-2013, 02:33 PM
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That's good info on the extractor and ejector. Now to find a barrel and a couple of magazines.
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Old 11-19-2013, 03:51 PM
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As has been stated above, you can just drop in an 9mm barrel and mag and you're good to go. My wife has been using the 9 conversion in her M&P40c most of this year with no issues. I took my son in law out for the first time last weekend with a 9mm setup in my 40 FS. Between the two of us we shot about 150 rounds, again, with no issues.
Midway has mags. If you are going to do this I'd get a couple of mags while you can.
http://www.midwayusa.com/product/862...lue?cm_vc=S014

Last edited by uechikid; 11-19-2013 at 03:58 PM.
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Old 11-19-2013, 04:09 PM
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Quote:
Originally Posted by Rastoff View Post
It absolutely will. The lock up between the slide and barrel is the critical component of accuracy. If the lock up is not tight, then it has the effect of the sights moving every time you shoot.

The M&P lock up is completely done at the chamber/slide interface. The barrel touches the slide at the muzzle, but that isn't the critical component of the lock up. Even so, the barrel should not move at all once the slide is forward.
There is an ever so slight difference in how the two barrels fit. The 9 barrel in the 40 slide has about a 1/64" amount of play. I would agree that this can affect accuracy, but I just put 75 rounds through mine and at 15 yards I was inside of 8" 68 times and I'm no marksman. For HD I'd say that's pretty good.
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Old 11-19-2013, 07:43 PM
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Quote:
It absolutely will. The lock up between the slide and barrel is the critical component of accuracy. If the lock up is not tight, then it has the effect of the sights moving every time you shoot.

SHHHHHH!
Don't tell that to my M&P40 -> 9 with the S&W Factory barrel. It doesn't know any better!

12 yards left target standing, right target sitting at the table with the gun resting on the table top.
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Old 11-20-2013, 08:43 PM
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OK I gather you can do the .40 to 9mm, how about the other way around?
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Old 11-20-2013, 09:01 PM
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I installed a 9mm factory barrel in my M&P 40FS and my wife used it the next day to qualify for her CHL.

I would not recommend converting a 9mm pistol to 40. That would require milling the sides of the 40 barrel to fit the 9mm slide, effectively reducing the thickness of the chamber walls. If I wanted that conversion I would buy a 40 slide assembly.
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Old 11-20-2013, 09:05 PM
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Sounds reasonable. Not that I can shoot a .40 anyway, the wrist is just getting too old for the sharp recoil.
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Old 11-20-2013, 09:17 PM
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9mm to .40 Shield has been done by a few members on here. Slight shaving of the .40 barrel to make it fit into the 9mm frame. But of course much like the .40 to 9mm, it'll perform without issue.

I dont know about the compacts or FS models.
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Old 11-21-2013, 02:40 AM
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Quote:
Originally Posted by mtnwinds View Post
I installed a 9mm factory barrel in my M&P 40FS and my wife used it the next day to qualify for her CHL.

I would not recommend converting a 9mm pistol to 40. That would require milling the sides of the 40 barrel to fit the 9mm slide, effectively reducing the thickness of the chamber walls. If I wanted that conversion I would buy a 40 slide assembly.
Why do you think that? As I posted above, the exterior dimensions of the two factory barrels are identical. At least for a full sized gun it should be just as easy to convert either way.
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Old 11-21-2013, 10:12 AM
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Rastoff, I was about to do this (40 barrel in 9mm slide), but I took a 40 shell, and tried to fit it into the breech of my 9mm slide. It will slide into the space between the ridge and extractor from the bottom, but not from the top. Sliding in a 40 barrel into the slide, and you can get it to seat ok, but the edge of the brass base just barely allows it to fit.

What this means is that any slop in the chamber to slide orientation may allow the brass edge to strike the ridge on the breech, and either deform the brass, or not allow it to go into battery.

To do this, the breech itself needs some widening.
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Old 12-09-2013, 09:33 AM
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a little late to this conversation, but also a new 9 owner, and was curious about the 9 to 40 conversion.is the lower the same? if i got a hold of a 40 slide and barrel and mag will it operate properly? or is it just not cost affective?
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Old 12-09-2013, 10:06 AM
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Yes, done it. Bought a 357 slide (didn't have 40 slide) and a 40 barrel from Midway shoots as good or better than the 9mm slide and barrel. Cost about $290 though.
Sad to say that S&W doesn't like their customers buying parts, They want you to buy GUNS. They are cutting off the supply of these parts. That is why people like Midway have limited or NO stock these days.
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Old 12-09-2013, 02:14 PM
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cool, thanks for the info. gonna shop around, see if i can find anything that will work for what im willing to spend. should have thought about this before i bought the 9, probably would have just grabbed a 40 and a 9 barrel
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Old 12-11-2013, 05:36 PM
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Hey didn't know any better myself.


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Old 12-12-2013, 01:27 AM
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I know this works on the compacts but will it work on a shield? Also, will they be selling .357sig barrels for the shield?

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Old 12-12-2013, 09:55 AM
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The frame is the same on the 40 & 9 mm Shields. Doubtful on the 357 sig though. Just not enough demand for them to do that


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Old 12-12-2013, 01:00 PM
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Quote:
Originally Posted by UpstateNY492 View Post
I know this works on the compacts but will it work on a shield? Also, will they be selling .357sig barrels for the shield?
Quote:
Originally Posted by sstewart View Post
The frame is the same on the 40 & 9 mm Shields. Doubtful on the 357 sig though. Just not enough demand for them to do that
S&W never made a .357 Shield so, there aren't any barrels no matter what. If they had made one, it would probably drop right into a .40 Shield just like it does for the full size.
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Old 12-13-2013, 10:27 AM
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Sorry I didn't realize this was a Shield specific discussion thread


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Old 12-13-2013, 02:11 PM
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I have a Shield 40 and also have stock 9mm barrel and mags for conversion capbility. It has fired flawlessly in both calibers for many rounds.

I also understand the reluctance of some Shield owners to perform this swap because S&W does not endorse it as safe. Not to mention that stock parts are scarce these days.

NOTE - I just rec'd an email minutes ago from KKM stating the following "We are hoping to have conversion barrels for the shields sometime this coming year." So there is hope on the horizin for those wanting 40 to 9mm conversion capability without anxiety.

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