If you are collecting opinions, I would like to respectfully disagree with grinder on the mechanism. Based on what I can see in the photos provided, the key to the failure mechanism is seen in photo #2:
Note that the fracture through the topstrap of the frame has a stepped appearance. This is caused by multiple cracks (in this case there appears to have been at least four) that initiate independently in the same area, then eventually coalesce. These are called ratchet marks and are considered characteristic of fatigue. The 45 degree crack extending from a corner is also typical of fatigue.
It appears that extensive use of the revolver at stress levels in excess of the endurance limit of the material initiated multiple fatigue cracks in the frame. Cracks in the topstrap propagated until the topstrap was almost entirely penetrated. When the next shot was fired, the remaining material of the topstrap fractured, producing the ridge of brightly fractured material along the top edge of the topstrap that we can clearly see in the photo. With the topstrap broken, the barrel was unable to hold together on its own and it split. The outward displacement of the barrel halves fractured the thin frame supporting the bottom of the barrel instantly.
Note that I am not saying your loads were excessive, but I am saying they were beyond what this particular revolver was capable of handling.
My qualifications are a metallurgy degree and 5 years spent as a failure analysis consultant.