I'll add another thanks Doc Drew for following up.
I may be seeing it wrong, but I believe the fired primer on the right hand side of the pictures shows possible signs of higher pressure than the left blown side. I think that gun has been eating a steady diet of over pressure loads for some reason or another. If all the right components are there, maybe you'll find a bushing throwing a heavy charge.
If a dimension of the gun is causing the pressure signs, you may find similar in the other barrel. I'd still guess that barrel integrity could be questioned , and you may find signs of a bulge. I don't think the red rust has anything to do with this mishap, but I think there're signs of black oxidation or defects that might be preexisting from before the barrel let go.
If they're willing to chat about it, maybe ask the metallurgist why the grain of the steel on these failures seems to be very coarse. Please also pass along thanks to the shooter/owner. Interested to read what you come up with when those reloads come apart. Take care.
