I understand all I need to do is put in a .357 Sig barrel from Midway. But I hear that maybe a new recoil spring is needed. My .40 is about 18 months old and in very good shape with no malfs. What's the real story?

I just replaced the barrel only. My .357 barrel is factory from S&W but that shouldn't make a difference.

No need to replace a recoil spring........

The recoil spring for a 357 SIG and the 40 caliber are the same as well as the mags, I did have some problems using my 357 about 3 out of fifty but I believe it was ammunition related. I also have the 357 barrel by Storm Lake for my compact 40 and have had no issues with it at all!

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59,M&P9,40,40C,357,(2)45,G26

Since this is a Smith and Wesson Forum, I was hoping to get some comment from S&W advising of the proper conversion method if this simple barrel change is unsafe. On another Forum I was told the conversion should only be made if the .40 is rated for +p ammom since the .357 Sig pushes pressure to 40,000 psi and the .40 only sees 35,000 psi normally.

Any comments?

I have a M&P 357 Sig with a spare 40 bbl that I bought from Midway. I was told by a S&W guy that everything was identical except the bbls and the markings on the slide. You should be good to go.

All I can say is that I have a M&P in 357 sig with a KKM 40S&W match conversion barrel and another M&P in 40 S&W with a Storm Lake 357sig conversion barrel. Both guns shoot either caliber reliably with the same factory spring. You can analyze the pressure differences and other variables to the n'[th degree but apparently the right answer is "one factory spring works just fine".
Buy the barrel and enjoy.

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Dave

Aren't the part numbers the same???

S&W shipped (or still does) a factory M&P with both barrels as a kit. They are the same.

One of my friends converted his M&P40c by simply buying a 357 barrel from the factory ($50) and dropping it in. We were amazed when we first shot it because it shot exactly to the POA with 125 grn Gold Dots. This is like having two guns in one.

I just called S&W for a Sig .357 bbl for my 40c, was quoted $80 plus shipping.

Thats still 1/2 the price of a Storm lake or KKM.

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Dave

Thanks very much for your responses. I think you have cleared this matter up. I will enjoy my new .357 Sig AND still be able to resurrect my trusty .40 when needed.

Brownells.com or Midwayusa.com barrels are S&W less expensive than buying from S&W and shipped quicker. The Drop in works flawlessly and if you obtain 9mm mags you can get the 9mm barrel from them too. Three guns in one. Mags are $23 from Botach.com and shipped free.

S&W M&P FS 9/357/40/45, 40PRO, 40C, All perfected with Apex!

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M&P 40, M&P 40C,

The 9mm slide isn't identical to the .40/.357. I have no idea if dropping a 9mm barrel into a .40 will work correctly and long term without possible damage. I'd respectfully suggest not trying.

Smith and Wesson along with a few aftermarket companies make a drop in barrell specifically for the M&P 40/357 full size, compact, pro and L models. Just like many of the other top gun manufacturers. You can go from 40/357/9. However you CAN NOT convert up from the 9mm as your statement regarding the 9mm slide is correct. The SLIDES are not the same.

I personally have the S&W barrels and they work perfectly. Over 1000 9mm rounds with no FTF/FTE.

S&W M&P FS 9/357/40/45, 40PRO, 40C, All perfected with Apex!

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M&P 40, M&P 40C,

I shoot my M&PC with all three barrels and they work great.

I just acquired a full size M&P40, and I will be getting the 9mm, and .357 barrels for it also.

not trying to hijack this thread but can you do the same thing with the 40 cal shield to convert it to 9mm.

Does the recoil spring need to be changed when converting from 40. to 9mm? Or do I just replace the barrel?

No spring change needed. it shoots fine with the 40 spring....

Thanks, I knew there was a reason I decided on the forty.

Also there is no SAMMI specs for a 40+P and thus no rating for a 40+P pistol.

As the others have said so well, all you need is a 357SIG barrel. Bill