I noticed the P320 slides aren't marked with a caliber. With the interchangeability of the platform, are all P320 slides the same, and just the barrel/recoil spring/sights installed into each slide are different?

My real question: Can I drop a standard 9mm P320 barrel into a .40/.357 slide and will it function?

In the P320, the 9mm barrel is slightly smaller in diameter than a 357 SIG or 40 S&W barrel. A 9mm barrel will fit into a 357/40 slide, but it does not achieve proper lockup at the muzzle. The barrel is free to move up and down slightly and although I would never try such a setup myself, I suspect that the accuracy would be very poor. I believe there’s also a good chance of excess wear or damage to slide and/or barrel with the barrel’s flopping around more freely than either was designed for.

quote:

Originally posted by sigfreund:
In the P320, the 9mm barrel is slightly smaller in diameter than a 357 SIG or 40 S&W barrel. A 9mm barrel will fit into a 357/40 slide, but it does not achieve proper lockup at the muzzle. The barrel is free to move up and down slightly and although I would never try such a setup myself, I suspect that the accuracy would be very poor. I believe there’s also a good chance of excess wear or damage to slide and/or barrel with the barrel’s flopping around more freely than either was designed for.

Great info, thanks!

Sorry to revive such an old thread, but I've searched and searched and can't quite figure it out...

Can one buy a Sig P320 in .40S&W/.357Sig and then convert it to 9MM? What additional parts would be required other than a barrel?

I'm sorry if this is a dumb question, but the Sig website has become... overwhelming. Or maybe I'm just getting old.

quote:

Originally posted by Light Fighter:
Can one buy a Sig P320 in .40S&W/.357Sig and then convert it to 9MM?

Some companies make “conversion” barrels that allow a 9mm barrel to fit a 357/40 slide. Bar-Sto, for example, mentions conversion P320 barrels for that purpose, but I can’t find anything more than that—a mention. I assume you’d have to call them. It’s possible that other companies also offer such conversion barrels. SIG does not offer conversion barrels, and as I mentioned, a factory 9mm P320 barrel would be a poor fit in a 357/40 slide.

When conversions for the SIG P226 or P229 were popular, most users said that they worked fine. I’ve never seen any discussion of whether that is true of the P320, however. Very few people have 357 or 40 P320s, it seems. SIG slides for 357/40 pistols are heavier than 9mm slides, and that will slow slide speed, but if a 9mm recoil spring is used that would help prevent any problems. In addition 9mm magazines would be necessary; 357/40 P320 mags won’t retain 9mm ammunition (in my experience). Another potential problem could be differences in extractors, but if I recall correctly all P320 extractors are the same now. Also, even when people were using 9mm ammo in 357/40 Classic line pistols the extractors worked okay.

If, however, you have the opportunity to purchase a 9mm P320 slide or a complete 9mm gun and then a 357/40 slide, that would simplify things and be more of a guarantee of proper functioning.
My first and still “serious” P320 was purchased as a 357 or 40 and then I got the other barrel to use the gun with either cartridge. Then I bought a 9mm P320 and an “exchange kit” from SIG when they still offered that so I could also use 357 or 40 as well as 9mm for training. Slides and barrels for 357 or 40 are currently unavailable from SIG, I believe.

I run a 9mm barrel in a Sig P239 with a 357/40 slide that would have the over sized extractor.

In theory with what you light fighter asked.... you would need to not only change out the barrel but the ejector spring as well as the slide so as to have the right extractor along with a 9mm magazine....

As I printed above it does work in my experience with the P239 and I suspect as noted it works in the P226 the only thing is I would not depend on my life with it.

Umm ....
I assume that Light Fighter is aware that there are many differences between the P239 and P320, but if not, I’ll mention it here.

And SIG ejectors don’t have springs; the P320 ejector is a fixed extension of the receiver, so there is nothing to change there. The extractors do have springs, but as SIG lists only one version for the P320, I believe they are all the same for the various models and don’t need to be changed when switching cartridges.
I also noted that the SIG site lists only one P320 extractor as well.