I think Johns right too. If I recall right from his web page. the entire turbine wheel broke off the shaft. So it was singing pretty fast and hitting lots of metal. Just about an explosion itself. And it wouldnt take a piece of metal very large to get into the chamber and do the damage it did. Yes the exhaust velocity is quite large. But I bet you could fire a BB into that exhaust port at any RPM, from a weak gun at that, and get it in there without any problem.

 

Bob Mears