The forcing cone doesn't care about cartridge length. At. All.

You will need to clean your chambers after using 38spcl, before swapping back to 357mag, because the 38's are shorter and will leave a fouling ring of powder and lead in the chamber between the case mouth and the chamber throat. If the ring of crud grows too thick, you won't be able to chamber the longer 357mag round at all, but more dangerous is the event where the crud is thin enough to let the cartridge seat, but thick enough to present a restriction for the case to release the bullet, spiking your pressure.

With a LOT of firing, you'll get a fire scorched ring in the chambers at the case mouth position, as the gases escape however briefly around the base of the bullet as it jumps the ~1/10th inch of extra diameter chamber into the throat. This isn't a big deal, other than a mental distraction, but it can cause sticky extraction with .357mag cases as the flame torched pits grab onto the case. Tap the ejector rod and it'll come right out, as designed.

Guys theorize about decreased accuracy due to chamber jump, but those are also typically the guys who can't shoot handguns well enough to tell if that were a real contributor or not.

Guys have been doing it since the mag came out in the 50's. There's no real down side, and lots of up side.