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Old 08-08-2013, 02:15 PM
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Default 9mm to .40 conversion?

So after doing some reading, I've found that the extractors for .40 & 9mm are the same, springs are apparently the same... So if one was to get a hold of a 9mm factory barrel & 9mm magazines (haha), would it theoretically function just as good in a .40 slide & frame as a factory 9mm? What am I missing here?
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Last edited by DocSunShine; 08-14-2013 at 07:07 PM. Reason: new spin on the question
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Old 08-08-2013, 02:20 PM
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This question is asked about once a month, and the answer is always the same: buy a stock 9mm barrel and a S&W 9mm magazine and enjoy. In a few instances, slight fitting may be required.
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Old 08-08-2013, 02:28 PM
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The same can be done with a conversion to .357 SIG except then different magazines aren't required as .40 S&W & .357 SIG use the same ones.
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Old 08-08-2013, 02:29 PM
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Quote:
Originally Posted by OKFC05 View Post
This question is asked about once a month, and the answer is always the same: buy a stock 9mm barrel and a S&W 9mm magazine and enjoy. In a few instances, slight fitting may be required.
So for carry, would a converted to 9mm M&P be good to go?
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Old 08-08-2013, 02:30 PM
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Mine has been working flawless for over a year now. I guess that means it'll work for u too.
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Old 08-08-2013, 02:36 PM
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Here you go:

Shield .40 convert to 9mm,how can you do it?

I tried to find the big thread but couldn't. I guess it expired.
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Old 08-08-2013, 02:39 PM
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Originally Posted by DocSunShine View Post
So for carry, would a converted to 9mm M&P be good to go?
If you are asking do I guarantee your work modifying a pistol, using whatever ammo you choose, will always function?

Man, I would not guarantee that with a brand-new custom shop pistol and factory Remington ammo!!

Any gun I am going to carry gets well broken in with what ammo I am going to carry, and I shoot, clean, and carefully check it at least once a month. I don't take anybody's word for anything on a gun I might live or die with!
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Old 08-08-2013, 02:47 PM
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Quote:
Originally Posted by OKFC05 View Post
If you are asking do I guarantee your work modifying a pistol, using whatever ammo you choose, will always function?

Man, I would not guarantee that with a brand-new custom shop pistol and factory Remington ammo!!

Any gun I am going to carry gets well broken in with what ammo I am going to carry, and I shoot, clean, and carefully check it at least once a month. I don't take anybody's word for anything on a gun I might live or die with!
Ah, wasn't asking for a guarantee, just asking if theoretically it would be good to go. Testing any gun and putting many rounds through any gun I consider a defensive gun isn't even a question.

I suppose the opposite, going from 9mm to .40 isn't possible?
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Old 08-08-2013, 03:16 PM
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Could u carry it for self defense (yes). Would i recommend it (NO). You are protecting your life and your loved ones. Dont risk the possible failure of a converted pistol. Use the .40 for self defense and use the 9mm for cheaper range time.

Going from 9mm to .40 is possible (at least with Shield). You must grind a tiny bit of the .4o barrel (tangs) down to make it fit into the 9mm slide. Since the 9mm slide is smaller here, u have to mod the .40 barrel or it will not fit. It's been done and a few members here are still running the conversion from 9mm to .40.
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Old 08-08-2013, 03:19 PM
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40 to 9 works fine for all the real posters I've read (including me)
9 to 40 does not work without modifying the slide.

the 40 mags work with 9mm in a few instances (not me), but using a factory 9mm barrel with factory 9mm mags in an M&P40 works flawlessly for me (about 3k rounds so far).
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Old 08-08-2013, 04:55 PM
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My 40C to 9mm conversion has been flawless for several months now. Originally I intended to use the 9mm barrel for range use only but it easily passed my benchmarks for reliability, most notably with the 17 round mags so it's currently on my nightstand in that configuration. Now I did just find a couple of 15 round .40 mags so when I get those I will swap it back to .40 and call it good.

The OEM barrel conversion for me was the single most important reason I purchased my 40C and I have not been disappointed.
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Old 08-08-2013, 05:11 PM
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I have made the 40 to 9mm swap for my Shield. It works perfectly, and I have not had one issue. I bought 9mm mags, but found that my Shield feeds the 9mm cartridges without issue, using the 40 mags. However some members have reported that they get a jam feeding the last round of 9mm, from the 40 mags. I have not had that issue, and I would think it is due to slight differences in the width of the mag feed lips.

9mm to 40 also works, except that the tang at the top rear of 40 barrel needs to be ground down about .012 to .013 inch on each side of the tang. The 40 to 9mm is a drop in swap as the 9mm barrel tang in more narrow than the 40 barrel tang, and fits into the tang slot of the 40 slide. Since the 9mm slide tang slot is more narrow (.407 inch), the 40 barrel will not fit into the 9mm slide. The tang width on the 40 barrel needs to made narrower, so it will fit. Nothing needs to be done to the slide. This was done by a forum member and documented how he did it with photos, however the photos no longer show. The following photos show where the 40 barrel tang needs to be narrowed, so it can be used in a 9mm slide. The photo shows the tang slot width of the 40 slide is .433 inch. I don't have a photo of the 9mm slide, but the width of the slide tang slot is .407 inch. The 40 barrel tang needs to be ground down to the width of the 9mm tang, and it will then fit into the 9mm slide. I have measured both the 9mm barrel and the 40 barrel and the only differences between the two barrels is: the bore diameter (9mm versus 40) and the tang width. There are no other differences between the barrels. I think the 40 to 9mm conversion is a better fit, as once the 40 barrel tang is ground down, the clearance is the same as the stock 9mm barrel, in regards to the slide slot width. When doing the 40 to 9mm swap, there is extra tang to slot width clearance of .026 inch, but no one has had any issue with that small amount of extra clearance. Accuracy is not affected.

Then you need 40 magazines, as the 40 cartridges will not fit into the 9mm mags. Remember the extractor and recoil springs are the same for both the 9mm and the 40, for all M&P models: FS, Compact, and Shield. You need to use the same barrels as your model, as they all have different barrel lengths.

Bob






Last edited by robkarrob; 08-08-2013 at 05:54 PM.
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Old 08-08-2013, 06:21 PM
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So basically, it makes the most sense to buy a .40 in M&P and just buy 9mm & .357sig barrels if you want to shoot those calibers... Interesting, I'd regret buying the 9mm CORE over the .40 except I now I have 3 9mm mags.
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Old 08-08-2013, 06:31 PM
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Took my .40 M&P to 9mm and works, had to borrow a friends magazine to try it out cause could not find 9mm magazines any place.
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Old 08-08-2013, 06:42 PM
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There's always someone asking 9mm or 40 S&W. The smart answer is get the 40, as all you need to do is buy a 9mm barrel, and you now have two calibers, for the cost of an $80 barrel.

Bob
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Old 08-14-2013, 07:08 PM
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Quote:
Originally Posted by robkarrob View Post
I have made the 40 to 9mm swap for my Shield. It works perfectly, and I have not had one issue. I bought 9mm mags, but found that my Shield feeds the 9mm cartridges without issue, using the 40 mags. However some members have reported that they get a jam feeding the last round of 9mm, from the 40 mags. I have not had that issue, and I would think it is due to slight differences in the width of the mag feed lips.

9mm to 40 also works, except that the tang at the top rear of 40 barrel needs to be ground down about .012 to .013 inch on each side of the tang. The 40 to 9mm is a drop in swap as the 9mm barrel tang in more narrow than the 40 barrel tang, and fits into the tang slot of the 40 slide. Since the 9mm slide tang slot is more narrow (.407 inch), the 40 barrel will not fit into the 9mm slide. The tang width on the 40 barrel needs to made narrower, so it will fit. Nothing needs to be done to the slide. This was done by a forum member and documented how he did it with photos, however the photos no longer show. The following photos show where the 40 barrel tang needs to be narrowed, so it can be used in a 9mm slide. The photo shows the tang slot width of the 40 slide is .433 inch. I don't have a photo of the 9mm slide, but the width of the slide tang slot is .407 inch. The 40 barrel tang needs to be ground down to the width of the 9mm tang, and it will then fit into the 9mm slide. I have measured both the 9mm barrel and the 40 barrel and the only differences between the two barrels is: the bore diameter (9mm versus 40) and the tang width. There are no other differences between the barrels. I think the 40 to 9mm conversion is a better fit, as once the 40 barrel tang is ground down, the clearance is the same as the stock 9mm barrel, in regards to the slide slot width. When doing the 40 to 9mm swap, there is extra tang to slot width clearance of .026 inch, but no one has had any issue with that small amount of extra clearance. Accuracy is not affected.

Then you need 40 magazines, as the 40 cartridges will not fit into the 9mm mags. Remember the extractor and recoil springs are the same for both the 9mm and the 40, for all M&P models: FS, Compact, and Shield. You need to use the same barrels as your model, as they all have different barrel lengths.

Bob





So is it possible to have a 40 barrel custom fitted to a 9mm slide, or have the slide customized to fit a 40 barrel (and maybe run 9mm conversion barrels)?
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Old 08-14-2013, 07:36 PM
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You do nothing to the 9mm slide. The only modification is to make the 40 barrel fit into the 9mm slide, in the tang width area, shown on the above photos.

Bob
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Old 08-14-2013, 07:43 PM
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Quote:
Originally Posted by robkarrob View Post
You do nothing to the 9mm slide. The only modification is to make the 40 barrel fit into the 9mm slide, in the tang width area, shown on the above photos.

Bob
Is this something most gunsmiths should be able to do, or is this something that would need to be sent out to a shop that specializes in this?
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Old 08-14-2013, 11:34 PM
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The forum member that did it used a dremel and a grinding wheel. I would suggest a 6 inch or larger bench grinder, using the side of the grinding wheel to grind off the metal. Carefully grind off one side of the tang of the 40 barrel, until you have removed .012 inch. Make sure you keep the grinding parallel and at 90 degrees. Then take .012 inch off the other side of the tang, keeping it parallel and at 90 degrees. The barrel should now drop into the 9mm slide. Buy some 40 mags and go shooting.

If you are not sure you want to do this yourself, take both the 9mm and 40 barrels to a machine or tool shop, that has a surface grinder. Ask them to make the tang width on the 40 barrel, the same width as the tang width on the 9mm barrel. Have them grind equal amounts off both sides of the tang, on the 40 barrel, until that tang is the same width as the 9mm barrel.

Bob

Last edited by robkarrob; 08-14-2013 at 11:38 PM.
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Old 08-14-2013, 11:47 PM
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Quote:
Originally Posted by robkarrob View Post
The forum member that did it used a dremel and a grinding wheel. I would suggest a 6 inch or larger bench grinder, using the side of the grinding wheel to grind off the metal. Carefully grind off one side of the tang of the 40 barrel, until you have removed .012 inch. Make sure you keep the grinding parallel and at 90 degrees. Then take .012 inch off the other side of the tang, keeping it parallel and at 90 degrees. The barrel should now drop into the 9mm slide. Buy some 40 mags and go shooting.

If you are not sure you want to do this yourself, take both the 9mm and 40 barrels to a machine or tool shop, that has a surface grinder. Ask them to make the tang width on the 40 barrel, the same width as the tang width on the 9mm barrel. Have them grind equal amounts off both sides of the tang, on the 40 barrel, until that tang is the same width as the 9mm barrel.

Bob
Well damn. I was kind of regretting buying a 9mm because of the .40s ability to shoot 9mm but not vice versa. But, this is very doable. Thanks for the great info.
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Old 08-15-2013, 12:16 AM
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Good info Rob. Sounds like I can use my CORE after all, just run irons on it and cut a .40 barrel a little. Kinda convoluted, but if it works, who cares....
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Old 08-15-2013, 08:29 PM
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One other thing I have not mentioned. The 9mm to 40 swap is a better swap, than the 40 to 9mm. The reason is by grinding the barrel to fit in the 9mm slide, you are making it a perfect fit, no extra side to side clearance. You end up with the same clearance as with the original 9mm barrel.

With the 40 to 9mm swap, the barrel is drop in, as the 9mm tang width is .025 inch more narrow than the 40 barrel tang width. The normal tang width to slide slot clearance is .004 inch per side. Since the 9mm barrel has extra side to side clearance of .012 per side, the total side to side clearance for the 9mm barrel in the 40 slide would be around .016 inch, as opposed to the stock clearance of .004 inch per side. Those of us that have made the 40 to 9mm swap have found no problems with that extra side to side clearance. No effect to any function of the gun, including accuracy.

Bob
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Old 08-15-2013, 08:45 PM
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Quote:
Originally Posted by robkarrob View Post
One other thing I have not mentioned. The 9mm to 40 swap is a better swap, than the 40 to 9mm. The reason is by grinding the barrel to fit in the 9mm slide, you are making it a perfect fit, no extra side to side clearance. You end up with the same clearance as with the original 9mm barrel.

With the 40 to 9mm swap, the barrel is drop in, as the 9mm tang width is .025 inch more narrow than the 40 barrel tang width. The normal tang width to slide slot clearance is .004 inch per side. Since the 9mm barrel has extra side to side clearance of .012 per side, the total side to side clearance for the 9mm barrel in the 40 slide would be around .016 inch, as opposed to the stock clearance of .004 inch per side. Those of us that have made the 40 to 9mm swap have found no problems with that extra side to side clearance. No effect to any function of the gun, including accuracy.

Bob
Yep, accuracy from the 40 converted to 9mm surely hasnt been a problem. Me and the ole lady both seem to shoot our converted .40 to 9mm better than we actually shot the factory 9mm. Weird how that works, but I guess the guns differ in trigger pull slightly and thats probably the main reason.
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Old 08-16-2013, 12:37 AM
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After shooting my C in 357, 40, and 9 I can say I favor the 9mm. After looking at some ballistic tests on modern hollow points, I really like the critical duty but thats me, I will stick with the 9.

I also own a fs 40/9 and both size 45s. I really like the 9. After I finish some work on my house I will be going with a core 9.
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