M&P 9C Factory Barrel In A M&P 40C

[jlh]

They're dimensionally, identical, except for "hole-in-the-barrel."....'Locks up fine....'Don't have any mags for 9mm yet, but the 40 mags work, except for not ejecting the last round, which extracts, but doesn't eject....'Hopeful that 9mm mags fix this.....Thoughts?......'On another note, has anyone had any dealings with "GunMag Warehouse," in Coppell, TX.....'Any problems/issues with them?...They have the 9mm mags at a good price.

 

[dsf]

I've bought quite often from GunMag Warehouse. Had M&P 45 ACP 12 round mags for $9.99 a while back. As advertised, slightly used but with strong springs, good follower.

Re the "40 to 9" I did the same, but IIRC there's a 9mm barrel specific to the change.

 

[mscampbell2734]

I've bought from Gun Mag Warehouse and never had any issues.

Regarding your barrel swap, going with the specific switch barrel will cure your last round eject issue. The problem is NOT magazine related.

The extractor is losing control of the empty case while extracting. The reason it only show up with the last round is because rounds in the magazine help support the empty case, hiding the problem until the last round.

The swap barrel will slightly position the chamber closer to the extractor to cure this issue.

 

[1sailor]

I used to have a first-generation M&P40. I bought a factory 9mm barrel for it and it worked great except for that last round ejection you mention. I ended up buying a couple of 9mm magazines and that seemed to correct the issue as it stopped happening. I probably put somewhere between 7,000 and 10,000 rounds of 9mm through it and I don't recall having any issues. This used to be quite a common conversion a few years back. In spite of the fact that it is often said that you MUST use a special custom barrel.

 

[125JHP]

I have the exact same last round experience as 1sailor... with my 1st gen M&P40c and a factory 9mm barrel.

However, I can use the 9mm mags when shooting as .40 and not have the last round issue.

 

[Saudade]

They're dimensionally, identical, <snip>

Well, they're not. Hood width is different. That's why 9mm barrels can fit in a .40/.357 slide but a .40/.357 barrel won't fit in a 9mm slide.

 

[125JHP]

I just checked my 40c gen 1, and the breechblock width is the same on both... .595"



but the hood width IS different...

.427" for the .40 and .3975 for the 9mm


I have seen hood width differences on different 9mm barrels for the same model (6906) but made in different years, so there is some variance somewhere, maybe in design revisions...

 

[AppStFan]

As has been previously mentioned, many folks have used a factory 9mm barrel in a .40 slide and have not had any issues. However I would suggest you err on the side of caution and use a dedicated .40 to 9mm conversion barrel such as one manufactured by KKM Precision and use 9mm magazines.