I had seen somewhere on the Internet where some bullets coating would react with powder - I forget the details.
I've had powder go off due to poor storage conditions - exposed to a hot wall repeatedly over many years, but it typically corroded through the case at the mouth and/or the primer - something turned to liquid and went looking for places to seep out of. Your's looks to be corroding at the base of the projectile where powder meets coating.
Last edited by mauserand9mm; 11/17/19.
