Were you using the maximum charge for the 110gr jacketed of 10.0gr Unique? If so, that would be about a grain over maximum for a 125gr cast bullet, and the 9.1gr max Lyman lists for that load was already the hottest one in the chart at 42,000 CUP. Even so, one grain over max alone shouldn't have caused this KB.

You can see that the cylinder failed instantly upon ignition, which to me is more indicative of a double charge. Is it possible a case was charged with powder just before you realized you ran out of jacketed bullets? Then you went and got the five cast bullets, charged the case again, and seated?