I use a Federal barrel in my G27 and had absolutely no problems. No other parts need to be changed. You might have to change sights if yours is adjustable, but other than that, there is no reason to do so.
I found I shot the .40 somewhat better, and I believe it is due to several factors.
1) I am more used to the 'feel' as it came from the factory.
2) I usually shoot at 30-40 ft. At that distance, I don't think you could see any difference in inherent accuraccy. At farther distance, my old eyeballs can't see that much of the target, so why bother?
3)The flash and noise of the 357 Sig is horrendous and should not create any real need to flinch, but I think I do. No physical reason, just mental.
(If you shoot at an indoor range, wait for the place to be empty and ask the operator to dim the lights. What a show. The flash is impressive. It may not do much, but it is impressive.)
