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asking my question a different way. I have been told twice that a .40 barrel will work in a P320 9mm platform. I have been told once that "no" it won't. With the Glock platform I decisively know you can convert down in caliber, with just a barrel (.40 - 9mm) but not up (9mm - .40) because the slides are slightly different where the muzzle comes out.
My question, are the 9mm and .40 slides different on the P320 platform and if they are why would 2 people tell me to " just get a .40 barrel"?
Thanks.
 

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A 40 S&W barrel will not work in a 9mm slide. Glock, SIG, HK, Walther, Ruger, HiPoint, Taurus, Lorcin, S&W, the list goes on and on.

Why someone would tell you to just buy a 40 S&W barrel, I have no clue. This I can tell you with absolute certainty: If you want to run your 9mm as 40 S&W, you need a 40 S&W slide. The diameter of the 40 S&W (10.0mm) is ~1.0mm larger than that of the 9mm. The breech face of the 9mm is not large enough to accept the larger 40 S&W (10.0mm) round.
 

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The Springfield XD is the only pistol I know of where you can drop a 9mm barrel in a .40S&W slide and have it work. Not sure if that’s the stock 9mm barrel or a conversion size barrel, though.

asking my question a different way. I have been told twice that a .40 barrel will work in a P320 9mm platform. I have been told once that "no" it won't. With the Glock platform I decisively know you can convert down in caliber, with just a barrel (.40 - 9mm) but not up (9mm - .40) because the slides are slightly different where the muzzle comes out.
My question, are the 9mm and .40 slides different on the P320 platform and if they are why would 2 people tell me to " just get a .40 barrel"?
Thanks.
 

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A 40 S&W barrel will not work in a 9mm slide. Glock, SIG, HK, Walther, Ruger, HiPoint, Taurus, Lorcin, S&W, the list goes on and on.

Why someone would tell you to just buy a 40 S&W barrel, I have no clue. This I can tell you with absolute certainty: If you want to run your 9mm as 40 S&W, you need a 40 S&W slide. The diameter of the 40 S&W (10.0mm) is ~1.0mm larger than that of the 9mm. The breech face of the 9mm is not large enough to accept the larger 40 S&W (10.0mm) round.
Is the inverse possible, IE p320 40S&W run a p320 9mm barrel and be good to go using the 40 slide?
 

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That’s my question as well. I’m purchased a P320 in 40 S&W for a really good deal. Since 40 S&W is about $0.10 more expensive per round than 9mm, I’d like the option to chamber down. It will also help my wife enjoy shooting with me ;)

So I’m guessing the 40 slide and breach face can accept a slightly smaller round, but not the other way around? I’m hoping I can get away with just buying a barrel and magazine in 9mm.
 

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That chart does not have the p250 or 320. Does it matter that the barrel will not be supported at the muzzle? Is the outer diameter of a 357 Sig barrel larger than the 9x19?
 

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Is the inverse possible, IE p320 40S&W run a p320 9mm barrel and be good to go using the 40 slide?
I just had a CCW student ask me that question, and I had to tell him IDK, but I'll check it out.

He has a compact .40SW and was asking whether he can run a 9mm barrel and 9mm magazine using the .40 slide. I really don't know -- but it seems like a reasonable question.
 

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I'm trying this now on my .40 compact. I ordered a barrel and magazines when I get everything assembled and out to a range I'll check back in.
 

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9mm will work in the .40 slide since the 9mm barrel diameter is smaller, but there will be a little slop to it. Does that matter? I guess you need to test out accuracy and see.
 

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You might be able to get a custom 9mm barrel that has the overall dimensions of a 40. But in the end probably cheaper to buy a second gun?

Edit: Bar-Sto make one, 40cal to 9mm conversion barrel, that had the dimensions of a 40 to eliminate the slop
 

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I just went to the gun room and tried swapping 9mm and 40S+W barrels, using a full size and compact version in each caliber, with the following results:
In neither case would the 40S+W barrel drop into the appropriate 9mm slide. The problem seemed to be the diameter of the 40S+W barrel in relation to the opening in the front of the slide as the barrel would fit in the hole, but would not drop to fit the breech face.

Both 9mm barrels easily fit the 40S+W slides, and while in battery, there was a bit of vertical play that would most likely manifest itself as sub-par accuracy, though I did not actually fire live ammo in the basement for obvious reasons. Also, in both cases, the striker would not release using the 40S+W slide with the 9mm barrel. At first I thought it might be because the full size was sent to Robert Burke for the completion action job, but the same thing happened with the compact, which is factory original.

I have tested swapping uppers on both guns, and that will work, which is the way the 320 was designed.

I also swapped uppers between 9mm and 40 S+W with the 45. While the 45 upper will fit on the 9mm and 40 S+W lower, and it appears to work, the 45 magazine will not insert into the FCU, so unless you want to feed individual rounds through the ejection port, it won’t work. The 9mm and 40S+W upper will fit the 45 frame/FCU, and appear to work(ie the striker will release), at least in my grip modules, neither the 9mm or 40S+W magazine would lock in the grip. The magazine catch would hold the magazine against a light pull, but a harder pull, or cycling the slide, would drop the magazine. It appears that enlarging the magazine cut would allow the magazine catch to hold the magazine, but I am not interested in possibly messing up a $40 magazine to find out, at least as long as I have adequate magazines for each caliber.

At least with my guns, it appears that the uppers and FCUs are interchangeable between the 9mm and 40 S+W( even if the barrels are not),but not with the 45 ACP.In my case, the 9mm and 40 S+W FCUs will not accept a 45 ACP magazine. YMMV.
 

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This is where my guess is where the confusion lies as to the OP being told he can just get a .40 barrel. Yes, you can convert a 9mm P320 to .40 or .357 it just requires a new slide/barrel/spring ie caliber conversion kit. One FCU and or grip module to run them all.
 

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While the 45 upper will fit on the 9mm and 40 S+W lower, and it appears to work, the 45 magazine will not insert into the FCU, so unless you want to feed individual rounds through the ejection port, it won’t work.
Aha! I knew it! I’ve been asking this question on here for over a year and all I ever got was crickets. So, all you need for a .45 is:

1) 45 slide, bbl, pin, spring (obviously)
2) wide slide release
3) 45 grip frame
4) 45 magazine

Now, will it fit in a safariland holster? Because, I’m not interested in buying another one of those ($$$).


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