Swapping M&P barrels

[aandabooks]

I recently took a M&P .40 on trade and since the .40 round doesn't really interest me I picked up a Storm Lake .357 Sig barrel. Now I'm thinking about adding a 9mm threaded barrel.

Does it have to be a conversion barrel or will any 9mm M&P barrel work? If it has to be a conversion barrel what is different between it and a normal barrel?

Here's a pic of the gun with the .357 barrel in it.

 

[Mark40]

I've looked into this for my 40c. I'm told the outside diameter is different for the factory 9mm barrel. I'm also told that S&W will not sell you one.

 

[Coastie762]

Factory 9mm barrels have a more narrow barrel hood (about .030 or so) than the .40. Otherwise their exterior dimensions are the same as the .40 barrel. Accordingly a 9mm barrel (of the correct length) will fit a .40 slide and function. A 9mm magazine is recommended for best function.

I've done it using a factory 9mm barrel in my .40 FS. Surprisingly that combination, using an older "slow twist" barrel produced some pretty good groups with 115 and 124 grain FMJs. YMMV.

Depending on what length you need, factory S&W barrels pop up at places like Brownells or Midway from time to time.

The conversion barrels are made with a wider barrel hood to reduce the side to side play and, in theory, provide greater accuracy.

Purchasing a factory barrel in another caliber had been pretty popular among .40 M&P users. I believe that S&W's restriction of sales had more to do with wanting folks to purchase another complete pistol than from potential liability issues.

 

[Rastoff]

Coastie762 has it right. The difference is in the hood dimension and how it matches the breech/slide.

This is the hood measurement of the .40 barrel:

This is the 9mm:

Here is the .40S&W barrel in the .40S&W slide:

Here is the 9mm barrel in the .40S&W slide:

Notice the gap difference.

So, the 9mm factory barrel will drop right in, but may have accuracy issues. If you're not concerned with the ultimate in accuracy, this won't be an issue. If 4" groups at 15 yards are OK, then dropping in a factory 9mm barrel will work just fine.

However, if you want the best accuracy you can get, the conversion barrel is the only way to go.

 

[Smitty357]

Most of us have been using the factory 9mm in the shield .40 for a very long time. Suprisingly i tend to shoot my .40 with the factory 9mm barrel better than i can shoot a factory 9mm shield. But of course this is likely because I have use to MY weapon and not the other one i was using. It just goes to show the factory barrel doesnt have any affect on the accuracy itself.

 

[Coastie762]

Rastoff, Excellent photos! In this case pictures are truly worth several thousand words.