I am sure this has been discussed before.  But my searching skills are horrible.  

I was wondering if they make a 40 to 9mm conversion barrel and if it is reliable, such as for carry?

Also would I need to get 9mm magazines instead?

And if there are barrels for the compact, would a factory 9mm barrel work?

Thanks everyone

I can't speak to the reliability, since I haven't bought one yet, but Storm Lake does offer conversion barrels in various configurations for the M&P. All are to convert .40S&W or .357Sig to 9mm. You can get them full size, compact, ported, threaded, etc.





You do need to have 9mm magazines to use with them.




http://www.stormlakebarrel.com/barrels

My Storm Lake barrel has been perfectly reliable, and at least as accurate, if not more so, than my factory .40 barrel.  The only thing I think some people would not like is that the barrel is stainless, but I kind of like how it stands out.

That is a straight drop in?  And all you woudl need is 9mm mags?  I am interested in this as I have a bunch of 9 that is sitting around doing nothing

My buddy just bought a stock 9mm barrel from www.brownells.com, used my 9mm mag and didnt have a problem out of the 200 rds he shot.
It was about half the price of the storm lake.

Has anyone else heard of doing this?  I was looking for a conversion barrel, and if I could save some money it seems like a good deal.

I know it has been a while since this has been posted, but if anyone has bought a replacement 9mm barrel and dropped it into the 40, and it worked, please let me know.

I have asked for one for Christmas.  I have read several people on other forums saying they have not had any problems, but none of them mentioned accuracy.  I will post again once I get it and put some rounds through it.

I have the M&P 9 full size and the 40c. When I got home last night I mic'd the barrels. They are exactly the same in respect to chamber width and length as well as barrels thickness (outer diameter) The only diff is the .40 has a thinner barrels (inner diameter). I placed the 9mm barrels in the .40 slide and it locked up tightly. I was able to chamber and eject a round easily as well. I would not shoot the weapon with the full size barrels on the compact frame, but will be buying the S&W 9c barrels.

I just recieved my S&W M&P barrel from Brownells. Cost was $75.00. It was just drop in and go. I was able to use the 9mm mags from my M&P full size. After making sure I was able to work the slide without any trouble I chambered and ejected 15 rounds without a hitch. It was now time to shoot it.

This is a group with the 40 S&W at 10 yards. 8 shots (only 7 in the target)


Switched to the 9mm barrel. 8 shots at 10 yards.

While I will never tell anyone to do the same as I did, I have to tell you how well it worked for me. I then went on to rapid fire over 100 rounds as rapidly as I could. I never had a malfunction of any kind.

bump

Based upon prior experience with Sigmas, I bet the 9mm barrel would shoot just fine in the .40 slide because the cartridge and the 90 degree surfaces working under spring pressure should result in reasonably consistent orientation while in battery. Try it and let us know!

The recoil spring/guide rod assemblies for the full size M&P .40, .357 SIG, and 9 are the same between them.

The recoil spring/guide rod assemblies for the compact .40, .357 SIG, and 9mm  models are interchangeable between them.