I'm considering converting 1 of my 2 M17 to 40 S&W using, CALIBER X-CHANGE KIT, P320 FULL, .40AUTO, then to 10mm by reaming the chamber to 10mm specs and change the springs

What are your thoughts? Has it been done? Am I going to die?

Maybe start with soft loads with pressures more like 40 S&W and work up slowly.

What's the weak link? The barrel, the grip module, the slide?

Do you think I'm the weak link and should keep the 40 S&W.

Magazine’s gonna be too short for the case length.

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Originally posted by copaup:
Magazine’s gonna be too short for the case length.

Did not think about that one. If there are no Sig 10mm mags it could be a show stopper.

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CALIBER X-CHANGE KIT, P320 FULL, .40AUTO

and has anyone ever actually seen one of these in the wild?

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Originally posted by hrcjon:

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CALIBER X-CHANGE KIT, P320 FULL, .40AUTO

and has anyone ever actually seen one of these in the wild?

550 returns from Google. All I checked are backordered. It may not even exist. Guess I'll call Sig.

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Originally posted by hrcjon:

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CALIBER X-CHANGE KIT, P320 FULL, .40AUTO

and has anyone ever actually seen one of these in the wild?

All of the CALIBER X-CHANGE KITS are out of stock. I purchased an M17 X-Change kit a while back to create my 2nd M17 because I had an unused FCU. I sold the kit on Ebay, with a small profit because of the shortage, to get the 40 S&W kit. I don't remember if the 40 S&W was out of stock when I got the M17 kit.

I don't think the 10mm would do you any favors. Consider converting it to 357 Sig.

The cartridge length puts it outside of the possibility of whatever the '9mm of the month' gun happens to be.

I don't think the P320 in 45 Auto would stay together with 10mm rounds ran through it either. If it would, Sig would never sell it could offer one up soon?

Glock was smart. They started with a 10mm and converted it to a 45. I found that it was easier to convert a Glock 21 to .38 Super or a Glock 22 to 7.65mm.

I had to modify the magazines myself. Only try it with a magazine that you wouldn't miss if it turns in to scrap. You'll have to tune the recoil spring as well.

If you make any progress, let us know how it goes.

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Originally posted by backlash:
It may not even exist.

They exist; I have one with both 357 SIG and 40 S&W barrels. But I bought everything several years ago before SIG stopped offering those two cartridge options in any form. It will be interesting to see if they ever come back. In fact I find it a little ironic that there are serious rumors that a 10mm P320 may be offered before it’s possible to purchase a new one chambered for 40 once again.

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Originally posted by .38supersig:
Consider converting it to 357 Sig.

Once you have the .40 kit, it's just a barrel away.

A P320 in 10mm would be ideal.

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Originally posted by .38supersig:
The cartridge length puts it outside of the possibility of whatever the '9mm of the month' gun happens to be.

Sorry, I don't understand this statement. I would be starting the 10mm conversion with a converted and tested .40 Sig p320. I could stop here but that would be no fun.

The only difference then would be the 10mm case is longer then the .40 so the chamber will have to be reamed to the 10mm spec. Brownells sells such a reamer and I have a machine shop.

I will need a magazine modified for 10mm. Will the .40 slide strip a 10mm round from the mag into the chamber? I don't know. Plus, what else have I missed? Need a lot of luck that it stays together.

I really need more research but at least I will have a .40 p320.

Usually 10mm guns are built on .45 frames, while .40 cal guns usually use 9mm frames. I don’t think a 10mm mag will fit in a 9/40 sized magwell due to the longer case length.

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Originally posted by sigfreund:

In fact I find it a little ironic that there are serious rumors that a 10mm P320 may be offered before it’s possible to purchase a new one chambered for 40 once again.

I've heard the rumors. If it's true it could be out before I can find a .40 conversion kit. A 10mm before a .40. What is Sig thinking. I'm sure the .40 would sell better then the 10mm. just not to me!

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Originally posted by backlash:
I will need a magazine modified for 10mm.

And how would that be accomplished starting with a 40 S&W magazine?

The published maximum overall cartridge length of the 40 is 1.135 inches; that of the 10mm Auto is 1.260", or 0.125" (1/8") longer. The front/back distance inside a 357/40 P320 magazine is 1.200", and there isn’t much extra room after a 40 cartridge is inserted. Just to be sure I tried a 10mm dummy round with truncated cone bullet from the Brownells set and it simply wouldn’t fit into the tube of the 357/40 mag.

And even if there were some way to modify the magazine to be large enough to accommodate a common 10mm round, then there would be the issue of fitting the oversized mag into the well of a standard P320 grip module.

If the rumored 10mm P320 ever sees the light of retail sale, it will obviously involve more than rechambering a 40 S&W barrel.

I have .40 P320's and .357 Sig P320's. I wouldn't ream out a .40 barrel to take a 10mm, even if the magazine and frame were large enough to accommodate the 10mm overall cartridge length.

I wouldn't count on adequate chamber strength in the .40 barrel, for the 10mm, and the conversion isn't taking into account slide mass.

I don't think the .40 slide will retract far enough to extract and eject a loaded 10mm cartridge.

Sig P320 M17, 9mm, 3 MAGS (no stock)
Total - $680


Sig P320 .40:

1 -CALIBER X-CHANGE KIT, P320 FULL, .40AUTO, 1-14 ROUND MAG - $400 (no stock)
1 -FCU - $350
Total - $750

I guess they do sell a .40 in kit form.

We need a CALIBER X-CHANGE KIT, P320 FULL, 10mmAUTO

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Originally posted by sns3guppy:
I have .40 P320's and .357 Sig P320's. I wouldn't ream out a .40 barrel to take a 10mm, even if the magazine and frame were large enough to accommodate the 10mm overall cartridge length.

I wouldn't count on adequate chamber strength in the .40 barrel, for the 10mm, and the conversion isn't taking into account slide mass.

I don't think the .40 slide will retract far enough to extract and eject a loaded 10mm cartridge.

Agreed. But I have an extra FCU so building a .40 looks like a good idea even if I can't go to 10mm. I'd like to have a .40 to run +P. Do you know if your .40 will run +P loads?

Baby steps:
Get the .40 conversion kit, if it ever comes available.

Go through my shop and find the magazine, and possibly a grip module, stretcher.

Then start worrying about chamber pressures.

Really, I was very serious about this 10mm conversion when I started this thread. But now, with all the help from this fine group of folks, I have doubts it can be done. I'll get to .40 and see what things look like.

ALL THIS IS SO EASY WITH THE 1911! .22, 9mm, .40 S&W, 45 ACP, 45 Super, 10mm, 38 Super, 460 Rowland......

This message has been edited. Last edited by: backlash,

If by +P loads you mean something that SAAMI has established as an upper chamber pressure limit for the 40 S&W cartridge like for 9mm Luger and a few others, it does not exist; i.e., there is no SAAMI +P designation for the 40.

Is it possible to load the cartridge to pressures that are above the maximum SAAMI limit? Sure? If we do that, will the gun function normally and never experience any problems? Possibly. Will the gun suffer damage to parts like the slide or receiver? Possibly. Will the gun blow up? Possibly.

SIG tells us that its pistols chambered for 9mm Luger may be safely fired with ammunition meeting SAAMI specifications, and therefore that includes +P loads. It does not, however, include ammunition rated by the manufacturer as “+P+” because there is no SAAMI specification for 9mm +P+. That doesn’t necessarily mean that a +P+ load will blow the gun up, but it does mean that if it does we’re on our own as far as SIG is concerned.

I’m pretty sure that the same would be true if we fired 40 S&W ammunition that was deliberately loaded to pressures that exceeded the SAAMI limit for the cartridge.

Dana Safety Supply
4729 Nelson Brogdon Blvd.
Sugar Hill, GA 30518
(770) 381-8633

Several exchange kits and grip modules in stock.

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Originally posted by backlash:
Do you know if your .40 will run +P loads?

What's a "+P .40 load?"

Other than marketing or the odd-man-out like Buffalo Bore, there's no standard for +P. It's not a real thing. Or a wise idea.

Is my P320 .40 approved for ".40 +P?" No, because there is no .40 +P.

While I have the P320 in compact and full size in .40 and .357 Sig, the full size now sit in TXG grip modules, and were purchased for shooting competition, with the idea of running light loads, not heavy ones.

So far as boring out a .40 barrel to make it into a 10mm barrel, it would be based on what engineering? What math has gone into that, based on the existing design of the P320 barrel? If the strength exists at R value now, when you change those chamber dimensions and increase the pressure, and move the stress risers or create others, and alter the dimensions in that chamber, what have you done to the margins? Have you done the math to support it? If you're not aware that there's no .40 +P, it sounds more like a guess that simple boring would change nothing but a little length, and thus be just fine...and guesswork is not the place to start such a project.

Further: an issue with .40's has been unsupported chambers or insufficient support, and blowing out the cases at the base of the cartridge. The "kaboom" so vaunted online isn't all myth; the pressure curve and spike is not the same as other cartridges, nor is it necessarily tolerant of increasing to greater pressures. Some powders are tolerant of position (small charge, large case), whereas others need to fill the case; the implications can be significant in the way the cartridge discharges, lock times, pressure peaks and timing, and the safety of that round being fired in one pistol vs. another. If a pistol was designed for one cartridge and his wildcatted to something else, it doesn't mean it's still safe.

As mentioned before, if you're increasing slide velocity or recoil forces, has there been an appropriate change in slide mass? Will the existing fire control unit, rails, slide, spring, and other components be up to the task, or do they need additional support, pins, frame strength, size, or other details that are far from trivial?

I have had several .40's blow out at the back of the cartridge. In two cases I recall off hand, it blew the magazine out of the pistol, and in one case blew the side of the pistol out, venting to my hand and back into my face, causing burns on my hand and face. Factory ammunition, standard pressure .40. Imagine the same thing with 10mm.

Max .40 SAAMI pressure is 35,000 psi, vs. 37,500 in 10mm. Where and how that pressure occurs is as important as the total value, as is the duration, the way it rises, etc. By comparison, .357 magnum Winchester has a max value of 35,000 psi.

.45 acp is 21,000 psi, and .45 +P 23,000.

It may be possible to do what you propose, though the frame and magazine isn't long enough to accommodate the 10mm cartridge, necessitating either a very short round with a light bullet, or an altered magazine and frame. As another poster noted, typically 9mm and .40 share the same size frames, while 10mm pistols typically share frame sizes with .45 acp; a bigger frame, bigger cartridge. Stepping from .40 S&W to 10mm is more than just adding a bit of length in the chamber.

As for a conversion kit, you'd probably be better off just buying a .40 pistol. If you have a spare FCU and want a .40 pistol, then you can pick up relatively inexpensive uppers on ebay; .40 isn't nearly as popular as other cartridges, and .40 slides/barrels can be had for not a lot of cost. Add the grip module of your choice, and there's your .40 "conversion."