(snip)

From my understanding, if I get a G22 I can get a G31 barrel and just drop it in and change that G22 from .40cal to .357sig just like that with nothing else needed. (and this works going from a G31 and putting in a G22 barrel also) And by just swapping out barrels I can swap out calibers, the same mags and everything else work prefectly because aside from the barrels, the rest of the gun is identical between these 2 models.
Is this correct? This bit is pretty consistent overall from different sources but I would still like confirmation.

That is correct. It should function perfectly, but you may notice a different point of impact for .357 ammo fired in a converted .40 weapon, as the sights may not be regulated correctly for the lighter/faster bullet, and the new barrel may sit in a slightly different position in the slide. Sometimes the sights are "close" with the new ammo, sometimes they are not, and may need adjustment.

The more controversion topic that I have heard many different things about is converting a G22 or G31 to 9mm. I know that I need 9mm mags, that the .40cal/.357 mags wont work for 9mm (supposedly g17 mags work in the g22/g31?)
I've heard that all I need to do to change these to 9mm is get a 9mm after market barrel designed for a g31 or g22 (availible from lone wolf).
I've also heard that I need the barrel as well as a new lighter spring (a g17 spring maybe?)
I've also heard that I would need a new extractor and ejector in order for this to work.
And I've also heard that I would need an entire new slide.

So in order to shoot 9mm from a g22/31 what do I need?
This would be for converting the pistol for cheap range shooting so 100% reliablility for 9mm isn't necessary, I just want to be able to effectively practice and shoot it.

To convert a .40 or .357 Glock to 9mm, all you should need is an aftermarket conversion barrel designed to make the 9mm work in the larger slide cutout area of the .40/.357 Glocks, and one or more 9mm Glock magazines that are the same length as your current Glock (G17 mags for full-size G22 or G31; G19 mags for a G23 or G32). In Gen3 guns, the springs are the same for 9mm/.40/.357 in the same size Glock; in Gen4 Glocks, there are lighter springs for the 9mm guns as they originally didn't function very reliably with same springs as the .40/.357 when using some types of 9mm ammo. You should not have to change the slide at all, providing you bought the correct aftermarket (non-Glock) barrel. The special barrel will take care of centering the smaller 9mm cartridge in the larger .40/.357 slide breech cutout area.

Instead of using an aftermarket conversion barrel, if you chose (as some people do) to convert your Glock by buying an entire Glock-manufactured slide/barrel assembly in 9mm, then you would have to change the ejector housing in your frame to make the Glock-manufactured 9mm slide/barrel assembly work on a Glock .40/.357 frame. This gives you the best reliability and all Glock parts (which some folks want), but the cost is much higher, and the conversion takes more time due to the need to change the ejector housing in the frame every time you go back and forth between 9mm and either of the larger calibers.

 

Thanks DJ.
Sounds pretty simple then, thats great.