Just to explain what I'm talking about -- three cases:
1. There's nothing in the barrel at all and there's a slight overload. At this point, assuming it's slight, the energy can probably exit the barrel without case expansion. Clear channel to exit.
2. There's a bullet in the barrel that responds to increase in load (slight overload) at a non-impeded ratio/speed (non-Molly). At this point, with a slight overload, the bullet would move out of the barrel fast enough to let the energy escape without case expansion.
3. There's a bullet in the barrel that responds to increase in load (slight overload) at an impeded ratio/speed (Molly). At this point, which a slight overload, the bullet can't move fast enough out of the barrel to let the energy escape without case expansion.
I was saying, "Maybe it's #3".