357Sig out of a Glock 23??

You're correct. All it takes is a barrel swap. Spring and magazines are the same. I have a Glock 27 that I bought a .357 barrel for. Functions flawlessly with either barrel. Here's a video of Hickok45 shooting a G23 with a .357 barrel:

http://www.youtube.com/watch?v=S4NeS0ezWMA

Can definitely be done and I do it via my Lone Wolf barrel. If you want to stay Glock, get the model 31 barrel. With the exception of the caliber markings, G22 40 cal magazines are identical to the 357 Sig ones. For that matter, the same is true for the G22 slide and receiver. The only mechanical/design differences between the G31 and the G22 are the chamber and bore. Other differences are 100% cosmetic.

ALL semi auto pistol barrels are "unsupported" to one degree or another. But "unsupported" is a misnomer. What's really the case is Glocks come from the factory with their chambers already "throated". Original Glock chambers were more generously throated to enhance chambering proficiency. With the advent of more standardized and higher quality factory ammunition, that factory throating could be, and was, reduced without degrading reliability.

I own two Glock with the "generous" barrel ... model 20 (1991) and model 23 (1993) both handle Buffalo Bore stuff with no bulges, smileys or anything else drawn attention to buy the gun rag bloggers. I've also loaded and fired tens of thousands of rounds of my own hand crafted ammunition. Stick to the know reliable and published data and you'll be fine. If you're looking to load one granule below chamber bursting you'll never be safe with any gun.

You can use a factory G32 barrel. Quite literally the only differences between .40 and .357 models are the bores of the barrels, the magazine tubes, and the magazine followers.

However early .40 frames didn't have the metal from the front frame rail insert extended forward to stop frame battering, which is necessary to shoot .357SIG.

G23 frames with serial number prefix CPU and after have the necessary reinforcement. G22 frames with serial number prefix CNX and after have the necessary reinforcement. If your .40 frame's serial number prefix is before that alphabetically, or the prefix is only two letters, it doesn't have the necessary reinforcement.

I have LWD 40-9 and 357 Sig barrels for my G23. I use G19 mags for the 40-9 barrel. No other mods. Both shoot great. The followers for a 357 Sig Glock are slightly different from the .40. A common consensus is that using .40 mags for 357 Sigs is better than using 357 Sig mags for .40's.

If this is an older gun, follow the advice to research which frames are safe for higher powered rounds.

The Glock 23 and 32 often use different magazines. Do they still? I don't know.

Don't bother. Lighter .40 ammo will have nearly the same effect as .357. Still I prefer heavy 180gn.