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Discussion Starter · #1 · (Edited)
I have been trying to learn about what is needed to change the size of ammo in Sig Sauer pistols. I'm a fairly new Sig owner so I need an easy explanation. Now that I own a P239 in 40, I am thinking about having the parts to make it shoot 9 or 357.

It's obvious that the barrel would need to be changed. Are the magazines different? Are there any other parts that would need to be changed to fire different size rounds?

Can you go up in size, say from a 9mm to a 40, or are there any other eliminating factors moving to different sized ammo?

I've even seen info on making a Sig shoot 22 cal. Is that advisable?

Finally, and most importantly, does changing ammo size affect or harm the pistol at all?

Thanks.
 

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rmak, generally it is said you can go down in caliber, but not up.
The .357Sig and .40S&W share case head diameter, and are generally interchangeable in double column magazines, some members have stated running 9mm ammunition in double column .357/.40 magazines, without too many problems, but again shouldn't be reliable enough for serious use. The 239 is a single column magazine, but Sig manufactures separate magazines for the .357Sig and .40S&W. I've seen people say that you can use the .357Sig in .40S&W magazines, but not the .40S&W in .357Sig magazines, this may be due to feeding guides in the .357 magazines being to restrictive for the wider projectile of the .40S&W.
The 9mm in the 239 has a dimensionally smaller magazine, and barrel from what I understand, that will fit, but the barrel is a loose fit in the larger slide, and the magazine a loose fit in the magazine well. Maybe fine for "range work", but not reliable enough for serious use, such as SD/EDC.
The .22 conversions were just that. Initially for cheaper practice, back when rimfire ammunition was cheap and plentiful. Most of these conversions required "premium" high velocity ammunition to operate efficiently. Sig still has them listed, but I don't remember them having them for 239s.
https://www.sigsauer.com/store/parts/conversion-kits.html?caliber=184
 

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What Willard Said.

The 357 to .40 is a Barrel and magazine shift. The .40 magazine will feed (Sometimes) the 357 bullet, but the .357 Wont feed the .40 bullet. Springs are the same.

For the .40 to 9MM, you need different magazine, Barrel and Recoil Spring.

I have a kit for all 3 calibers for mine. Both were initially .40, and I changed the Rear Sight from a #8 to a #10 (Old Bullseye shooter. Need to have a 6 O'Clock Hold).

at 15 yds, everything fits in the same 3X5 card with a Bullseye hold.
 

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Willard nailed it with his explanation. I have a P229 Legion in 357 Sig that I enjoy shooting and several months ago I purchased a 40 S&W barrel for my Sig and it was a perfect drop in and it shoots perfectly. Not a lover of the 40 S&W, but my son runs one and therefore I load that round and have about 1000 once fired cases. The 40 is an expensive round to buy if you don't reload. Just my two cents.
 
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