Can anyone tell me what is now required to change from 9MM to 357SIG?

Complete upper/slide/barrel, locking block, and mags?

All P226 locking inserts are the same.

I converted a P229 DAK .40 to .357 Sig by just changing out the barrel. I would imagine you would just need a barrel, mags, and springs.

When I was buying my 229 years ago, I was told I could change a P229 or P226 .40 to a 9MM and .357 sig by just a barrel change.

The 9mm could not be converted the same way because the slide was narrower and would not take the .40 and .357 sig barrels.

I turned down a P226 9mm at a good price for that reason. I am sorry I didn't grab the P226.

Things might have changed that was around 2005

I have three barrels each for my P229 and P239

I think you would need to change the whole top end as well, barrel, slide and probably magazines. The breach face would be different between the two. If you were going the other way, from .357 to 9mm you could get a conversion barrel, I did that with a P229, and that is all you would need.

you need a 40S&W conversion kit with a 357 sig barrel or a 357 sig conversion kit. Unfourtuately the supply has dried up and who knows when sig will make more with the backlog of guns they are working on.

Osage County Guns is a pretty good vendor but they are out. You could contact them and get on a list!!!

The 9mm and 357/40 slides are different, however the frame of the p226 is the same for both. You will need a new slide, recoil spring, recoil guide, barrel, firing pin, firing pin spring, safety lock, firing pin roll pin, safety lock spring, ejector, ejector roll pin, ejector inner and outer spring, and #8 front and rear sights.

Of these parts between the 9mm and 357 sig the following parts are different:

Slide for .40/.357 sig
Recoil Spring for .40/.357 sig
Barrel .357 sig

You could remove all of the other parts in your 9mm and install them into a new .40/.357 sig slide however realistically those parts are fairly cheap. I would just get a whole different set of parts for a 357 sig slide and keep your 9mm slide built encase you want to shoot 9mm or sell it off.