Is it possible and what would do it?
Will a Sig 9mm barrel do it?

I recommend you read the discussion here (ignore the post that says it can’t be done):

https://sigforum.com/eve/forums...0601935/m/5250042224

It’s been reported by several people that it’s possible to simply install a standard 9mm barrel in a P226 originally chambered for 40 S&W and it will function properly. The barrel isn’t designed to fit the 40 slide, but evidently that doesn’t seem to matter. If I were doing it, I’d use the 9mm barrel with a 9mm P226 recoil spring and magazines, but they may not be absolutely necessary. There are, however, no guarantees about any of this.

Before people started doing this, the usual way of converting from 40 to 9mm in a P226 was to get a conversion barrel from Bar-Sto or another company.

I just picked up a 9mm Silencerco barrel, 9mm recoil spring, and some 9mm mec-gar mags for the pistol in the above link. Hand cycles and ejects just fine. I'm taking it to the range later this week to give it a test run.

Edit to Update: Ran 100 rounds of PPU and Federal 9mm ammo through the above setup. No failures of any kind.

100 rounds isn't a large enough sample size to declare it good to go for everyone, but I'm optimistic.

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