If I remember correctly Steel cased rounds do retract/relax from the shape of the chamber as fast as brass. Brass also being softer. Check the head of the steel case to see if the extractor tore up the edge when it didnt eject. From what the fella said its most common in the carbines with the short barrels. Guess cause the gas ports are a little further back and the gas pressure is still peaked. I had a full size A-2 AR-15 years ago and it didnt care what it ate.