I talked with a Hodgdon tech for 2 hours one day about this. They do know what is going on and can duplicate it on command with a 243Win. Like I said they call it a high pressure excursion. SEE happens in a navel gun. Like the 16" on the old battleships. The 6.5x55 was the one that everyone quotes. The long eroded throat makes this a possible. Same thing with the 243. The bullet is sent out of the case and is stopped from not enough pressure to make it past the throat. That bullet is now a bore obstruction as the pressure is building out of the design of the powders burn rate.I dont care what you call it or refuse to call it. I dont care what you think is happening inside the chamber, in which no one can see, and no one knows for sure.
If you google Secondary Explosion Effect you will get all the info you need on exactly this. Even if you refuse to concede to this name.
Call Hodgdon. I did.