Even though the sprag in a 904 is far less likely to spin in the case, the outer ring can crack and have basically the same results.
The lighter drum in the 904 is just less likely to explode.
Best of luck getting it to critical mass. Will a cracked drum explode, yes, because it is already compromised. A good one has to spin around 18-19K+ to hit critical mass. Not many street guys are getting there.
In all the years I've been around this stuff, the number of 904 drum explosions = 0
