Converting a Sig P239 .357 to a 9mm?

bigdude01 · August 13, 2012, 12:07 AM

Is it possible to just buy a 9mm barrel and mags from sig and convert my .357sig P239 to a 9mm?

Or could I purchase a 9mm barrel from sig and still fire .357sig rounds from it? The barrels should be the same diameter, correct?

Auto426 · August 13, 2012, 01:20 AM

You should be able to find a 9mm conversion barrel for your 239 that should pretty much drop into your gun, and along with a set of 9mm mags, allow you to fire 9mm. You can't use both rounds in the same barrel because the cases for each round aren't the same size, and therefore the chamber in each barrel is different. See the comparison below:

(Please ignore the typo in the picture, I didn't create it.)

NJgunowner · August 13, 2012, 08:24 AM

Err, no. You can't shoot 9mm in a .357 sig barrel.

TunnelRat · August 13, 2012, 10:09 AM

Quote:

Or could I purchase a 9mm barrel from sig and still fire .357sig rounds from it? The barrels should be the same diameter, correct?

bigdude01 · August 13, 2012, 01:43 PM

Does the 9mm and the .357sig round have the same bullet diameter, .355"? I was under this assumption.

TunnelRat · August 13, 2012, 02:00 PM

357 SIG is a necked cartridge. The case width is wider than the bullet, more than normal. A 357 SIG round won't chamber in a 9mm.

NJgunowner · August 13, 2012, 03:07 PM

The .40 s&w and .357 sig factory barrels can be swapped in the same gun. NOT the 9mm. (might need a new recoil spring too, don't remember)

And don't confuse that statement with .40 and .357 sig barrels are can fire either. The .40 uses .40 rounds, .357 sig uses .357 sig rounds.

Just go with what is stamped on the barrel.

Barsto makes conversion barrels if you're really interested.

Sharpsdressed Man · August 13, 2012, 05:27 PM

I have done the conversion, so I know it works. I installed a 9mm barrel into a .357/.40 SIG P239, with a 9mm magazine, ande it worked perfectly. You cannot convert a 9mm P239 to .357 or .40, as it is slightly smaller (frame/mag well, for starters), but for the money for the barrel and mag, you can do it. When first contemplating this conversion, I called SIG, and they stated it may or may not work, depending on the contact being made on the wider breech face by the extractor, but my gun's tolerances were such that it worked just fine. The 9mm mags are just a tad narrower than the .40/.357SIG mags.

August 13, 2012, 12:07 AM	#1
bigdude01 Junior Member Join Date: March 7, 2010 Posts: 6	Converting a Sig P239 .357 to a 9mm? Is it possible to just buy a 9mm barrel and mags from sig and convert my .357sig P239 to a 9mm? Or could I purchase a 9mm barrel from sig and still fire .357sig rounds from it? The barrels should be the same diameter, correct? Last edited by bigdude01; August 13, 2012 at 12:25 AM.

August 13, 2012, 01:20 AM	#2
Auto426 Senior Member Join Date: November 24, 2007 Location: South Louisiana Posts: 1,323	You should be able to find a 9mm conversion barrel for your 239 that should pretty much drop into your gun, and along with a set of 9mm mags, allow you to fire 9mm. You can't use both rounds in the same barrel because the cases for each round aren't the same size, and therefore the chamber in each barrel is different. See the comparison below: (Please ignore the typo in the picture, I didn't create it.) __________________ *"Si vis pacem, para bellum"* - If you want peace, prepare for war.

August 13, 2012, 02:00 PM	#6
TunnelRat Senior Member Join Date: May 22, 2011 Posts: 12,212	357 SIG is a necked cartridge. The case width is wider than the bullet, more than normal. A 357 SIG round won't chamber in a 9mm. __________________ Know the status of your weapon Keep your muzzle oriented so that no one will be hurt if the firearm discharges Keep your finger off the trigger until you have an adequate sight picture Maintain situational awareness

August 13, 2012, 08:24 AM	#3
NJgunowner Senior Member Join Date: February 13, 2009 Location: NJ Posts: 1,254	Err, no. You can't shoot 9mm in a .357 sig barrel.

August 13, 2012, 01:43 PM	#5
bigdude01 Junior Member Join Date: March 7, 2010 Posts: 6	Does the 9mm and the .357sig round have the same bullet diameter, .355"? I was under this assumption.

August 13, 2012, 03:07 PM	#7
NJgunowner Senior Member Join Date: February 13, 2009 Location: NJ Posts: 1,254	The .40 s&w and .357 sig factory barrels can be swapped in the same gun. NOT the 9mm. (might need a new recoil spring too, don't remember) And don't confuse that statement with .40 and .357 sig barrels are can fire either. The .40 uses .40 rounds, .357 sig uses .357 sig rounds. Just go with what is stamped on the barrel. Barsto makes conversion barrels if you're really interested.

August 13, 2012, 05:27 PM	#8
Sharpsdressed Man Junior member Join Date: June 21, 2009 Location: NE Ohio Posts: 1,176	I have done the conversion, so I know it works. I installed a 9mm barrel into a .357/.40 SIG P239, with a 9mm magazine, ande it worked perfectly. You cannot convert a 9mm P239 to .357 or .40, as it is slightly smaller (frame/mag well, for starters), but for the money for the barrel and mag, you can do it. When first contemplating this conversion, I called SIG, and they stated it may or may not work, depending on the contact being made on the wider breech face by the extractor, but my gun's tolerances were such that it worked just fine. The 9mm mags are just a tad narrower than the .40/.357SIG mags.