Barrel split all the way to the end? I'd be suspicious of a longitudinal seam in the barrel. I'd love to see the fracture surface(s).
Or could be a double charge.
I never liked having much space in the case. Dabbled with reduced loads in the .375 H&H years ago, and after having hangfires, wound up using tufts of cotton balls to fill the space. The loads shot extremely well, so they worked, but I probably wouldn't use them today.
