Conversion of M&P 9

[BobRowe]

I'd like to try a conversion of my M&P 9 to either .40 S&W or .357 Sig. I assume that, at the very least, I'll need a new barrel and new magazines. What else would I need?

Since the .40 S&W and .357 Sig cases are larger in diameter than the 9mm case, will the slide breech face and extractor on the 9mm slide work OK on the .40 and .357? How about the ejector?

This would be used as a carry piece, so absolute reliability would be needed. If I can't achieve that, I won't even attempt it.

Has anyone here done this conversion?

 

[Houdini1953]

The only conversions I know of are to take an M&P .40 and then buy a standard 9mm barrel and also the 357 sig but you can't go bigger than 9mm only downsize from the 40 caliber!

 

[OKFC05]

Forget it. The .40/.357 cartridges won't work in a 9mm breechface.

The 9mm usually work in a .40, even though the casehead is a sloppy fit.

As far as absolute reliablity for carry, then forget about all conversions IMHO. I want that casehead to be a SAAMI fit in the breech.

 

[remat457]

You could buy another complete upper assembly

 

[SMMAssociates]

Bob:

If you have the option, swap the 9C for a 40C, then pick up a Storm Lake barrel for the 9mm conversion (and a couple of 9mm mags). The .40 version will be 100%, of course. Can't speak for the 9mm conversion, but the 9mm Storm Lake barrel is designed to be used in the 40C slide.

Or, you can do what I did.... I had a 40C with no thumb safety, and picked up a 9C with one. I decided I wanted a thumb safety on the 40C, because that's my "around the house" carry, and being a 1911 guy, wanted compatibility. Just swapped slides and magazines....

Not a cheap solution, but at the time I actually wanted the 9C too. Just didn't expect the thumb safety....

A very good reason for "buy two, they're small" ....

Regards,

 

[Arkie45]

Bob:

If you have the option, swap the 9C for a 40C, then pick up a Storm Lake barrel for the 9mm conversion (and a couple of 9mm mags). The .40 version will be 100%, of course. Can't speak for the 9mm conversion, but the 9mm Storm Lake barrel is designed to be used in the 40C slide.

I got a Storm Lake 9mm conversion and mags for my 40c...shoots like an absolute dream! Not to mention takes only 30 seconds to change. I shoot a lot tighter groups with the 9mm than with the original .40. Like getting another gun for just $150.

 

[hoochrulez55]

only thing ive heard is you can swap out your 40 barrel and assembly for 9mm equilvalents. i dont know what else you need though.

 

[SMMAssociates]

hooch:

All you need is the new barrel and some magazines in the new caliber....

You can use an S&W "factory" 9mm barrel, but it's not supposed to work nearly as well (due to the breech face differences) as the aftermarket (most people seem to recommend Storm Lake) barrel, which is designed to drop into the .40 slide and compensate for the differences.

Again, you can't put a .40 barrel into a 9mm slide and expect it to work well, if at all (I never tried that), but you can put a 9mm barrel into a .40 slide. However, the aftermarket barrel is the better choice.

(And the new magazines .)

I can't speak for accuracy, point of aim v.s. point of impact, etc. Should be more than good enough for SD training (cheaper 9mm ammunition). (For SD, 6 or so rounds into a 6" circle at about 30' is adequate. Even if the gun will shoot minute-of-nothing, there are so many other factors involved that will help you mess up that it's not worth worrying about anything better than that.)

Regards,

 

[jdizzel1209]

i have the 9mm c and got my wife the 357 sig with 40cal barrel and the 9mm wont fit in the slide of hers and the 40 or 357 wont fit in my 9mm slide but i cant say on the full size m&p

 

[Lost Lake]

hooch:

All you need is the new barrel and some magazines in the new caliber....

You can use an S&W "factory" 9mm barrel, but it's not supposed to work nearly as well (due to the breech face differences) as the aftermarket (most people seem to recommend Storm Lake) barrel, which is designed to drop into the .40 slide and compensate for the differences.


However, the aftermarket barrel is the better choice.

Maybe I'm stoopid, but isn't the breech face part of the slide? All the barrel does is hold the bullet and guide it. The inside of a 9mm barrel is smaller than a .40 but the outside is the same.

I have heard of many more problems with conversion barrels than factory barrels when going from .40 to 9mm.

Do a search on converting from .40 to 9mm and find the thread with all the micrometer readings comparing a factory .40 to a factory 9mm.

 

[SMMAssociates]

jdizzel:

The .40 slide should properly accept the 9mm and (maybe) .357 barrels, AFAIK, but the aftermarket barrel is supposed to be a better fit. The 9mm slide might accept the larger caliber barrel, but it's not going to work....

Or something like that....

Lost Lake:

It's my understanding that the important part is the placement of the extractor, and of the firing pin. The larger breech face shouldn't matter as long as everything else lines up. So, the Storm Lake barrel sort of makes believe it's a 9mm where things must line up, and makes believe it's a .40 to properly fit the slide.

This makes the location of the firing pin and extractor pretty critical, but there's probably enough slop in the latter to make things work. The idea of matching the breech face is probably related to accuracy - having the barrel/chamber fit the breech face is part of the lock-up....

Regards,
(I gotta get one.... )

 

[Lost Lake]

Stu,
Are you saying the Storm barrel is drilled off center?

The firing pin and extractor are on the slide, so only off-center drilling could affect the operation of either.

It will be very easy to tell if the Storm barrel is centered.