You may very well be getting good repeatability out of yours, but every "presto-chango" barrel swap deal I've read about specifically states that extraction may present problems. I'll have to find one and scan it in if you want proof of that too. It's quite possible that the extractor will do it's job, but I sure as hell wouldn't count on it to function on a defensive pistol. Besides, I'd say practice with what you carry, or you're just burning powder. If you're trying to find a cheaper way to become proficient with your carry weapon, switch to bulk ammo in the same caliber, as shooting high quality defense loads can be expensive, but switching to a .22 conversion kit or even a 9mm conversion kit and practicing defensive shooting when you'll be normally carrying a .357 Sig, well, you aren't going to shoot them the same.:watching:
Try taking a 40 or 357Sig (which use the same breech face) to using a 9mm bullet. And when the weapon won't cycle with repeatability, or blows up in your face.. you can tell me, if you can still speak.