Bar-Sto says on a .40 to 9mm conversion for P226/9:

For Sig firearms the 229,226. You only need to change the barrel and use 9mm magazines. On the 239 you only change the barrel and can use the 40 but not the 357 sig mags. On all these you can get factory 9mm mags for those.
No spring changes needed. The breech face is fine and the extractor on these type of firearms springs over far enough to catch the case head and extract reliably.

That's the official line they have in their FAQ's section. Anyone ever actually done it without a slide conversion kit?

The Bar-Sto drop ins generally do not require any smithing to ensure a proper fit. Sometimes a little "fitting" is required and would best be accomplished by a qualified smith. If you get the larger (.357/.40) from the onset, you only need to get the conversion barrel and mags to shoot 9mm. If you start with the 9mm set up, you WILL have to get a slide as well. The reason is that the slide dimensions are more robust for the larger calibers due to pressures and recoil forces generated by the rounds. The standard 9mm slide will not stand up to the forces as they have not been designed to and thus do not have the strength and integrity to do so.

Simple answer is:

.357/.40 to 9mm conversion = buy conversion barrel and mags
9mm to .357/.40 conversion = buy conversion barrel, mags AND a slide.

Need the straight poop for more validation/verification, call SiG Customer Service. Their number is listed on their website and is toll free.

The P239 is an odd critter in this process as the mags for .357 and the ones for .40 ARE different and cannot be used interchangably like can be done with same caliber applications in the P229 or P229 models. I cannot speak to the conversion applications as they apply to the P250 as I don't have much first hand experience or knowledge with it. I've shot it a few times and in 9mm and .40, I prefer the SP as far as the polymer frame models go in comparison.

So there would be absolutely no problem buying one of those barrels and dropping it in a P226 that was originally chambered for .40 S&W? You have personally seen someone do this, or have done it yourself?

I just want to be double plus sure, otherwise I'll end up buying the P226 in 9mm instead of .40.

Thanks again, and sorry if I'm asking you to repeat yourself =)

Originally Posted by Jaster83

So there would be absolutely no problem buying one of those barrels and dropping it in a P226 that was originally chambered for .40 S&W? You have personally seen someone do this, or have done it yourself?

I just want to be double plus sure, otherwise I'll end up buying the P226 in 9mm instead of .40.

Thanks again, and sorry if I'm asking you to repeat yourself =)

Not exactly. They are generally drop in items, but occasionally the 9mm barrels require a little fitting so they seat properly. Bar-Sto would have more information on this. I'm not sure of the percentages but they would have that info. I have seen people do this swap at the range a few times. I do not own this set up as I don't care for .40 in anything I've tried it in to date. I haven't been and won't be swayed by the hype. I am most proficient with 9mm and can place rounds on target at ranges up to 50 feet. I have my .45 as something different, but my CCW's are all 9mm. My reply in the "Great Caliber Debate" is shot placement trumps all. Recent news items prove my point as there were two men shot and killed with a .22 pistol by an 8 year old.

SiG wouldn't say it can be done if it wasn't designed that way from the onset. That is why they explicitly state that you cannot go from the smaller 9mm setup to the larger calibers. You clearly have questions on this matter. Contact Bar-Sto and SiG. Their information is available on their respective websites and I'm sure they will be happy to answer anything you ask them about.

Originally Posted by Growler67

Recent news items prove my point as there were two men shot and killed with a .22 pistol by an 8 year old.

I thought it was a rifle. Either way, it's a horrific and sad event. This kid managed (as I heard it on the "news") to shoot both adults multiple times with a single-shot .22 rifle. Sad...

-Jeff-

Originally Posted by BeefyBeefo

I thought it was a rifle. Either way, it's a horrific and sad event. This kid managed (as I heard it on the "news") to shoot both adults multiple times with a single-shot .22 rifle. Sad...

-Jeff-

Might be. I'm going off an early report stating it was a single shot pistol. I assumed Derringer-like. I haven't kept up with the story and so I was going off of what was initially reported. Horrific to say the least and over discipline that was measured out a day or two prior. Seems like parenting and coping skills didn't mix in much to this point in the upbringing but I am heading off course here.

BOT - shot placement over caliber. Debate is over.

I have dropped a 9mm barrel into my P226 40/357 without any problems. I have also changed the recoil spring when doing so, but I don't think it is needed. I will say that it is not recommended, but I am trying to find a 9mm slide that will fit my 226 frame. If you end up buy a 40/357 framed gun and want to attach a 9mm upper, keep in mind that the newer frames of the 40/357 guns will not mate with the original 9mm slides. Just make sure your 9mm slide does not have a serial number starting with a U1 or U0.