M&P 9mm Barrel in .40 Slide Assembly??

[DrewBegley]

Ok, I have an M&P Compact .40 caliber and want to shoot 9mm through it. I have a few questions on how to do so:

First, I've heard you MUST use a ".40 to 9mm Conversion" barrel in order for it to lock up tight enough. Is that true, or is it a minimal safety/performance concern?

Second, I've heard the other end of the spectrum where you can just drop in a factory 9mm barrel into a .40 gun and it works just fine. Obviously I'm iffy on that, at least that it'll have the same accuracy and reliability.

And lastly, I plan to can it eventually. Can I drop in (or fit) a Stormlake/KKM 9mm threaded barrel and it be good to go or do I need a .40 to 9mm threaded barrel (if they even make them)?:banghead:


Any info is much appreciated!

 

[Walt Sherrill]

It probably depends on the specific de,ign of the gun and the barrel lugs.

Generally, the diameter of the .40 barrels are larger than 9mm barrels for similar models, and using the smaller-diameter barrel in a .40 slide leaves some SLOPthat could cause inconsistent lockup.

That said, I've seen videos on YouTube where Glock users who seem to really know the guns and their capabilities, swap out barrels and the accuracy is not greatly degraded when the swap is done. But, I don't know whether there are wear issues using the smaller barrel in a gun. Then, too, accuracy is not the only concern: there can be headspace issues, and extractors might not extract properly.

For many guns, a conversion barrel from several different providers is relatively inexpensive, and addresses things like headspace and extraction in their design. (I have a Glock 35, and also have an EFK Firedragon conversion barrel that allows me to shoot 9mm rounds -- including lead bullets -- if I want to do so.)

Why risk possible damage and potentially less-than-optimal accuracy? Get a conversion barrel and do it right.

If you're going to buy a barrel anyway, there's absolutely no reasonable argument that favors the purchase of a non-conversion barrel. (The conversion barrels generally cost the same as the standard non-conversion barrels for the same family of weapons.)

.

 

[Manco]

First, I've heard you MUST use a ".40 to 9mm Conversion" barrel in order for it to lock up tight enough. Is that true, or is it a minimal safety/performance concern?

The regular 9mm barrel won't fit properly. It may sort of work sometimes, I don't know, but it's not the right part--just use a conversion barrel, please.

You'll also need a 9mm magazine, by the way.

Second, I've heard the other end of the spectrum where you can just drop in a factory 9mm barrel into a .40 gun and it works just fine. Obviously I'm iffy on that, at least that it'll have the same accuracy and reliability.

You can drop in a factory 357 SIG barrel in order to shoot that caliber (fits and works perfectly), but the same is not true for 9mm--do so at your own risk.

 

[DrewBegley]

haha, thanks guys. I'm working off what I've read in other forums on the barrel and have also seen guys drop in 9mm factory barrels into their M&P .40 with a 9mm mag and it seems to shoot just fine. I'm not doing that.

Mainly just wanted to hear about what all is involved in the swap. I plan to get a threaded barrel, but can't seem to find a .40-9mm conversion barrel with threads OR a .40 threaded barrel for the M&P Compact.

p.s. not too hot on buying a 250 dollar storm lake...