# .40 M&P to 357 sig



## TheReaper (Nov 14, 2008)

Do I just need to swap the barrels ?


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## undrgrnd (Jul 10, 2008)

TheReaper said:


> Do I just need to swap the barrels ?


it should just be that simple but I would contact smith and wesson to be 100% sure


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## TheManRSW (Jan 21, 2009)

I have the .357c and was told by a customer service rep that a .40c barrel would just "drop-in". I've also been told by others/gun shop/other forum folks that it's just that easy. I'm trying to get a factory .40c barrel from s&w, but it seems they are out of stock at this time.


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## literaltrance (Dec 24, 2008)

Disclaimer!!! I am no gunsmith!!! I have never owned a S&W M&P let alone made any custom changes to one. I think the most appropriate venue to ask such a question would be the manufacturer's forums. Having said that...

_Typically_, going between 40S&W and 357SIG is just a barrel swap. The casing sizes are virtually identical with regard to the breech face. I think one of the biggest factors to keep in mind is when going from 40S&W to 357SIG that chamber pressures are going to increase, thus you may want to consider getting a slightly stiffer spring.

But you happen to be going the other way (357SIG -> 40S&W) so you'll see a slight decrease in chamber pressures. Generally speaking, having a slightly stronger spring for the job is better than having a slightly weaker one. You might notice casings eject a foot or two shorter than normal, but as long as its clearing the firearm and your body consistently I'd say you're fine.

[Edit]: Read this data how you will. It tells me the M&Ps must be pretty tight if the 9mm comes with a 16lb factory spring and the 40S&W comes with a 17lb spring. I imagine 357SIG is either 18lb or 19lb, and 1-2 lbs extra resistance shouldn't hurt any "weaker" calibers using it.


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## TheReaper (Nov 14, 2008)

Thanks for the good news and I will post on the S&W forum and get their opinion.


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## TheReaper (Nov 14, 2008)

It is a simple barrel change and I'm ordering the barrel today for $110. I did notice that the 357sig ammo is more expensive than the S&W.40.


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