I was in Doug Wells shop in Missoula when he was working on a Rossi 92, 357 that had chain fired in the tube. It had a mix of cast SWC and cast RN. His theory was that the cartridges were at an angle and a high primer set things off. SWC was under the ones that fired. There were 3 that fired and three that the pressure blew the end of the loading tube off and the cartridges landed on the ground. IIRC three left in the tube.