I haven't seen this question asked before so, here it is.

I want to change my .40S&W compact to 9mm. I have a 9mm barrel, but it's the full sized one. It fits in the compact gun, but will it do any damage if fired in that condition?

Enquiring minds want to know?

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I've never shot it like that but I have put a FS barrel in a compact. The barrel does feel a little loose because the stock barrels have a larger OD at the muzzle end, but I don't know if that would be a problem. Accuracy may suffer but I think it would shoot without a problem. I've attached a picture of a 4.25" M&P with a 5" barrel installed, you can see the wear on the larger portion of the barrel.

Attached Images

IMG_20140713_201504_294 (Small).jpg (65.3 KB, 107 views)

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M&P9 will work in 9c

I too have put my FS 9 barrel in my compact. Looks like bkreutz's. I'm confident I would never deliberately shoot it like that.

Why would you want to?

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Wisdom comes thru fear . . .

So I can shoot 9mm. I thought it was obvious, but I guess it wasn't.

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[QUOTE=Bkreutz;138057662]I've never shot it like that but I have put a FS barrel in a compact. The barrel does feel a little loose because the stock barrels have a larger OD at the muzzle end, but I don't know if that would be a problem.

I'm no expert, but I think I read somewhere that this larger OD assists in barrel lockup. You probably already have slight side to side play at the rear if its a factory 9 in a 40 slide. Add the loosness up front, and that just seems like a bad situation waiting to happen. Personally I'd buy a correct tight fitting conversion before I'd try this, but that's just me.

If it does, the affect on lock up is really small. Look at this:


As you can see, there is a lot of space around the muzzle when the slide is closed.

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I think the best thing is to try it and see what the results are.. at worst you would have a pattern instead of a group.

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Minimize the variables

Rastoff,

The lock up doesn't happen at the very end. It's about a 1/4-1/3" further down. Look at your current barrel and you should see the wear marks. You should also see it 'flare' in that same area. That's the forward lock-up area (At least that's how it is on a FS 40).



So with the difference in barrel length (4.25 vs. 3.5") you're definitely out of tolerance for the forward locking surface. My educated guess is that the same concept would apply if you wanted to put a 5” pro barrel in a slide designed for the 4.25” barrel.



Hopefully you can see in my pics the ‘flared’ area that starts before the muzzle

But does the barrel move around when you try to move it with your fingertip? I've tried that with every single pistol I own - even well used ones - and none of the barrels will move when in lockup.

Would a 40C fire and cycle with a FS 9mm barrel in it? I am sure it would. Would it do damage to either the 9mm barrel or the 40 slide? I personally wouldn't want to find out, but feel free to try... and let us know after 3000 rds.

I bought 2 Stormlake 9mm conversion barrels. IIRC $92 for the 40C and about $110 for 40FS. I use them mostly for range practice, but I wouldn't hesitate to carry with them. I thought about getting slightly longer barrel for either - and I could've done that with a threaded or compensated barrel - but I ultimately decided to go with the stock lengths.