What is involved in converting a .40 Sigma to shooting 9mm?
I was basically thinking about getting a 9mm barrel to put in my .40 Sigma and possibly some 9mm mags if the .40 mags won't work and then firing 9mm out of it to have a dual caliber pistol that i can shoot the cheaper 9mm out of.
Has anyone done this?
I've seen where a 9mm barrel can be had for $75 to $100.
I don't know if I need to change out the recoil spring as well..
thanks in advance

Here's what you need that is different betwen 9mm and .40 Sigma: frame, magazines, slide, barrel................but, good news, the recoil spring is the same part #.

I have both. The 9mm magazine just falls back out of the .40 frame, and the .40 magazine is too wide for the 9mm frame.

This question gets asked about once a month, but don't feel bad, at first glance they look the same size---until you measure.

ok, thanks. Guess that saves a buck or 2. I guess I'll just have to get a 9mm Sigma in the future.

Do you know if anyone makes a barrel that has the outside dimensions of the .40 barrel but with a 9MM hole in it? Or possibly anyone that makes an aftermarket 357 Sig barrel for it?

Not any more. The factory .357 Sig Sigma barrels were solid, but the aftermarkets had some problems. I would be leery of any leftover aftermarket Sigma barrels.

The cheapest way to get the switch-barrel setup is to buy the M&P, which has factory barrels availble in .40 and .357. They drop right in , with no fuss.

9mm conversions to either .40 or .357 will always have the challenge that the 9mm case head is just enough different from the other 2 to somewhat mismatch at the extractor.
Not impossible, but not always reliable either. A fellow shooter spent the price of a gun trying to make one conversion work, and it never did.
One poster on this forum took a 9mm Sigma barrel, chamber reamed it to .357, then carefully fitted to his .40 slide and extractor: about 6 hours careful work. He reported it functioned correctly. Neat bit of precision gunsmithing, but expensive if you have to pay for it.

There was a post on either this forum, The High Road, or The Firing Line from someone who bought a 9mm Sigma barrel from Smith and Wesson and a 357 Sig chamber reamer from somewhere and made their own 357 Sig barrel for their SW40VE. This allows you to use the same magazines.

I'm tempted to try this myself just for the heck of it. I have access to a machine shop and could bore my own.

All the Best,
D. White

I wish we had a conversion kit to make are Sigmas into .22s

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Don't look, reload and shoot!

I don't know if EFK makes conversion barrels for Sigma ....I got one for a Glock 22 to convert it to 9mm and it works great,just change barrel and magazines...look for it at EFK barrels.

I guess he does not believe OKFC05. A Sigma is not a Glock 22.

this. would safe lots of money on range trips

Yea, I was looking for fairly simple and cheap. I guess it would be a lot simpler and cheaper to just pickup a used Sigma 9mm for 250 or so. Oh well, I tried. I'm not that greatly enamored with the 357 Sig cartridge as I think its a solution looking for a problem to solve when you can get 135gr .40 loads and do whatever you needed the 357 Sig to do.
I was more interested in a 9mm conversion for the cheaper ammo to shoot.
I have a Ruger 22/45 to shoot the cheaper 22LR ammo along with a single six to shoot 22 or 22 mag.
I guess in the long run it would just be cheaper to use the money to buy more $14/box of Federal .40 ammo to shoot at walmart.

I was probably the one who asked last month! I have since went out and bought a second sigma for my arsenal.

Looking at maximum average chamber pressures of 9mm, 40 S&W and .357 sig suggests that the idea above just might be dangerous:

9mm = around 30,000 PSI
40 S&W = around 23,000 PSI
.357 sig = around 39,000 PSI

removing metal from a chamber designed for the 9mm pressures and sticking in a round which may produce up to 10,000 PSI more pressure than the chamber was designed for (even before you removed the metal) doesn't sound like a really great idea to me. Let me stand well clear when you take this modification to the range. The numbers above are just averages taken out of some reloading databooks. I don't have the SAAMI specifications at hand.

. . . you could get one of these 22LR's . . .

Well, the results are in. I physically inserted a 9mm mag into a .40 frame, no go, there's about a 32nd of an inch difference in width with the 9mm being the smaller and the it's a little longer. I didn't have any measuring tool at the time or I could've mic'd it LOL.

I loaded the .40 mag with 9mm, swapped slides and barrels on the .40 frame to the 9mm and voila, instant 9mm. I fired between 50 and 75 rounds with the new config and it functioned perfectly. Wow, I now have a new range gun with dual caliber config in case I run out of one or the other LOL. I can also load 12 9mm rounds into the .40 mag.

If you can find ammo. I've had better luck finding 40 S&W and 9 mm Luger than .22 in any form. I'm down to ~250 rounds of 22 LR with none in sight.

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Semper Fi

All this talk of coverting a 9mm and .40.

Maybe it's me but it seems by the time you buy a barrel and slide and whatever else. You could just the complete gun of the other caliber. That would eliminate all headaches and possible gun malfunctions. That's just me though.