Did you remember to back the seating die out 0.135" so the crimp shoulder would be higher by the greater length of the magnum case? That's almost two full turns of the die body (1.89 turns, to be exact). I'm thinking you left it set for .38 Special so it was the crimp shoulder that buckled your case. The bullet should be no issue. I used them in .357 for years in a DW 15-2.
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