You will only be able to load 38s if your die set is specifically marked 38/357. I don't know of any dies currently made that are not made to load both, but your post specifically asked about using a "357" die. If the die is marked 357, you probably won't be able to seat the bullet properly and crimp, as the crimp shoulder will be set for the .357 case, which is .115" longer than the 38 case, if memory serves.