I have had a WTB up in classifieds for a while looking for a .380 conversion kit. It looks like no one has one but I just saw something of great interest. Is it possible to run a .380 barrel in a P320? Understand you would need the correct magazine and I am not sure about the RSA. I have found a source for a P250 .380 barrel only. Thanks!

The outside diameter of a .380 barrel (0.471") is smaller than the outside diameter of a 9mm barrel (0.552"), so a slide based on .380 barrel dimensions would be necessary for reliable operation and consistent accuracy.

A .380 recoil spring is markedly thinner and has fewer coils than a 9mm recoil spring.

A .380 slide for a P250 also has lightening cuts that are absent on a 9mm slide, so differences in speed and momentum between the two slides would impair reliability.

Thanks for the info, sir – I kinda suspected there was a fly in the ointment. There are a couple of places on GB selling “conversion kits“ with just a .380 barrel and magazine. They say it will convert both a P320 and P250 to .380. I should have known that, like too many sellers on GB, they are full of it ...

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

Sig's factory conversion kits for the P250 and P320 have always included a slide, or more precisely, all parts for a whole gun except the Fire Control Unit.

My guess is the GB ad you saw was made up of parts from CDNN (barrel $20, magazine $10, and grip module $20). The hints that it is not an original factory exchange kit include the lack of a slide and the fact that the grip module does not have a mag release button.

Last dumb question - will the .40 and .357 barrels work in the 9mm P250 slides? .40 barrels are cheap on GB and I have the ammo and dies ... Thanks!

From a P250 owner on another forum:

quote:

Sorry, no, a 40 (10mm) barrel will never fit a 9mm slide. The barrel extension will never fit the slide breech face.

So I'm hearing you guys say, it's not a real conversion kit (of course), and that a 380 barrel in a 9mm slide would be unreliable (certainly) and inaccurate, but here's my question: Would it physically work? The P250 parts are so similar. Would it function, even if poorly?

Bump

Can anyone clarify from actual experience: do the parts fit and function to any degree?

Is that 380 set up just going to perform poorly or is it dangerous/non-functional?

I would not pull the trigger on such a mishmash of parts to see if it would work.

Agreed, it seems risky. But I don't know; I wish it would work just for the novelty.

If it's actually dangerous, why are these things advertised and sold with P320 on it?

quote:

Originally posted by Thumper44:
If it's actually dangerous, why are these things advertised and sold with P320 on it?

To the best of my knowledge, the only top-end parts SIG sold in one caliber claiming they would fit another caliber were .40 S&W and .357SIG.

The barrel is 20 bucks and the mags are 10 at CDNN. Why don't you just buy one and try it? If I still had my SC slide I'd do it.

You could at least test the lockup and cycling of rounds safely without firing. If it seems promising you could have a gunsmith check things out before firing, or if you like to tinker you could go all MythBusters and set it up in a sled with a string.

Too bad they don't have a Compact .380 barrel for that cheap.

quote:

Originally posted by JBird679:
Too bad they don't have a Compact .380 barrel for that cheap.

SIG did not make a compact-size .380 barrel. The .380 models labelled Compact and Subcompact both used the subcompact-size barrel and slide.

quote:

Originally posted by JBird679:
Why don't you just buy one and try it?

I think I will. If I do, I'll report it step by step. Also good advice to check with a gunsmith. I know a SIG armorer in my church who could give some guidance also.

I ordered one of the .380 SC barrels from CDNN and it arrived last week. It fits into my 250 9mm slide perfectly at the chamber end; the barrel hood is a perfect-looking fit with no slop. But, as gc70 mentioned, the barrel diameter is way undersized for the 9mm slide and it is a very sloppy fit at the muzzle. I like the .380 P250 so much I was just hoping to have a P320 in .380 too. Well, at least I have a spare barrel ...

I had forgotten from the OP that the question was about converting a P320, which involves even more issues than it would to put a .380 barrel in a P250 9mm slide.

The P320 is a striker-fired pistol that is cocked when the slide closes. A P320 recoil spring has to be strong enough to pull the slide forward, pick up and chamber a round and cock the striker. At issue is whether a .380 round generates enough recoil to compress a recoil spring that is strong enough to power the return half of the slide cycle.