Some years ago I had an incident of delayed ignition while shooting skeet with a gun in 28 ga. I was shooting a 12ga. gun with Briley subgauge tubes, and the shells were reloads in Remington cases. The powder was WW540. I called for the target, and upon pulling the trigger, got a click-bang hangfire. When I removed the tubes after the round, I found a bulge and split at the forward end of the stainless steel chamber portion of the tube. I sent the tube to Briley for repair, and they replaced the chamber portion of the tube with a longer than standard chamber piece.
I don't know what caused the hangfire, but I suspect that it was a hull that I had previously fired in the rain that still had a drop of water in it when I reloaded it. The primer had enough force to start the shot and wad out of the hull, then the powder ignited, causing a pressure spike. There was no damage to the gun, and I continued to use the repaired tube for several years.
