The difference in holding the gun muzzle down without and with a Dacron filler.
(Same case used)
It's harder so see in a pic but it is evident just the same that without filler and with the powder down against the boolit (on the left), the pressure is higher.
These 'accidents' that occur very rarely - how do we know the filler itself was not 'accidently' left out and that the damage was due to the absence of the filler in a load intended for a filler? (Of course, that would make the danger just a real! Or worse.)
P.S. There is no difference in the appearance of the powder residue!