Interesting write-up and assesment by Dutchman, onthe Castboolits article, along with a rough translation.

The point is raised that there is no rust apparent on the broken surfaces visible, of the breech block.
It does not seem a stretch to me that the part was rusted due to contact with blood, and that it would have been aided somewhat by any cleaning that would (may have?) taken place during surgery to remove it

From the looks of those rounds, recovered at the scene, I would not be too surprised if it was determined to be an issue of black powder that had been rattled around until it wa just fine powder.

No matter that hypothesis. Going to the range with such a mixed bag of ammo, of obviously poor condition, just seems a poor choice to have made.

It will be of interest, not just to me, I think, if the follow-up report trickles out. I know that I would like to know the findings.

Cheers
  Trev