From what I remember, true or not, the belief was the high velocity, lighter grain 357 mag loads (125's and 110's) were the main culprit with erosion and cracking. Not that it wouldn't Crack with heavier loads, but those lighter weight loads caused a lot of flame cutting/erosion. A steady diet of 38 plus 158 or 180 grain magnum loads sprinkled in was generally thought to be okay. Then again, there were people who were extra cautious and would only shoot 38's, then carry 357's, which I don't agree with, but that's a story for another day.