rifle detonation again

[Martini2]

As mentioned the incident is regrettable and thanks to the photos provided some sense for possible cause(s) are coming to light. I'd refer interest to book "Down Range Data" by William T. Falin , Jr. Not that you have to agree with this gentleman's entire ideas but here are some facts. Mr Falin was the Chief ballistician at Accurate Arms. He was "solely responsible for XMR-5744 becoming a standard in that line". pg. 23 "Thus , I had the the opportunity to establish strict performance criteria during product development." " My goal was to produce a smokeless propellant that was as position insensitive as is feasible". The above quotes are from Mr. Falin's text and everyone is recommended to read same. He went on in other chapters to advocate loads WITHOUT wads and particularly "Dacron fiberfill" for one. The amount of 5744 necessary to replicate Black Powder velocity
is 25 grains or less. So indeed a double load could fit in 45-70 case.
It would be very interesting in ruptured barrel's case if bore has one or two slugs in residence. I.E. did shootest have misfire followed by second round? Lastly, this rifles manufacturer as well as other Italian imports have a very specific printed disclaimer packed with their rifles. Essentially NO HAND LOADS are allowed and use of same voids warrantee. However print does point to factory ammunition. Therefore their product should be proofed for those pressure specs.