A friend has a .40 S&W caliber P320 Compact and would like to convert it to 9mm. I know that I when I converted my P250 from .40 S&W, I only needed to swap out the barrel, recoil spring system, and magazines with those designed for 9mm. Does the same apply for those wanting to convert their .40 S&W P320s to 9mm?

Thanks in advance for the advice!

P320s chambered for 9mm, 357 SIG, and 40 S&W all use the same grip modules and fire control units. Switching among the three cartridges requires the proper magazines, slides, recoil spring assemblies, and barrels. Between 357 and 40 requires only a barrel change.

I use all three rounds with the same “lower.”

Added: I just realized you didn’t mention the slide.
P320 357/40 slides are different from 9mm slides. In addition to the breech face dimensions and how that affects the extractor interface, the former are heavier than 9mm slides. Perhaps most important, though, is that 357/40 barrels are slightly larger in outside diameter than 9mm barrels. Checking just now, a 9mm full size barrel fits into a 357/40 slide, but not surprisingly, it’s a little loose. That combination might work, but I suspect the accuracy would be poor, and perhaps there would be chambering problems.

While it's true you will need a new magazine, slide and barrel when doing stock. Bar-Sto sells a conversion barrel for the P320 that allows you to use the same slide and will only require new mags. Though, for the price of their barrel you can find slides and barrels on ebay for about the same.

The conversion kit is sold out at Sig's website but you can find them for less on GunBroker with a simple search. I wanted to sell a compact 9mm slide barrel and recoil spring assembly last year here and received no interest. Still have it.

Wish your friend was local to me as I would be willing to work a deal on buying his .40. Then he could just buy one in 9mm.

quote:

Does the same apply for those wanting to convert their .40 S&W P320s to 9mm?

No. A P320 is just like a P229 in this regard. A .40/.357 slide and barrel have different dimensions at both the muzzle and breech face than a 9mm slide and barrel.

Option 1, factory supported: Acquire a 9mm slide, barrel, recoil assembly, and magazine(s).

Option 2: Acquire a conversion barrel, recoil assembly, and magazine(s).

A conversion barrel is manufactured to the external specs used for .40/.357 but the internal specs used for 9mm.

quote:

Originally posted by ah3:
A P320 is just like a P229 in this regard.

Actually, not “just like.” When trying to change cartridges with the P229 there is also both the locking insert issue and the fact that original 9mm P229 magazines and 357/40 P229 mags are somewhat different as well. P320 9mm and 357/40 magazines differ in their feed lip dimensions, but they are all the same width and fit into the same grip modules.

since in another thread I was sort of trying this in reverse with a P226 I decided to look at my P320 Compact in 9mm. Seems the barrels for the p320 Compact are the same for the older P250 and I had recently bought a 40 cal conversion slide/kit for the P250 but wanted it to be 357 and so ordered a 357 barrel from Sig for a P320 compact. This actually does work in the P250. My point is I looked and the two barrels... 357 & 9mm are a different size outside and the 9mm slide for the p320 will not work with the 357/40 barrels...

Thanks all for the advice. I'm posting a WTB in the SF Classified section for a P320 9mm Compact slide (milled for optical sight), recoil spring assembly, and a 21 round magazine.

I only have a non milled slide so I can't help you but try doing a search on gunbroker for "P320 complete upper" to see what pops up. A lot of dealers break pistols apart and sell the parts and assemblies separately to boost their profits. You may find a deal that way.