There are a few false statements above. Most new dies will be marked for both 38 Sp and 357 mag. Same goes for 44 Sp/44mag. Such as these http://www.midwayusa.com/product/418...ial-357-magnum
So you can reload either with the same set of dies.
As far as die adjusment goes, the first die(resizer) does not need to be adjusted going between 38 and 357. Once that's set you leave it.
For the second die(expander), the expander plug needs to be raised up higher for 357, or lowered for 38. Same with the third stage (seater/crimper). But as others have mentioned, you can setup the 2nd and 3rd dies for 38sp, then use a spacer/washer to raise the two dies up so you don't have to readjust for 357.
Does that clear things up?