I think a lot pf folks are forgetting a key word here INERTIA puller. What ever force is driving the boolit out of the case will also drive the primer deeper into the pocket since the same force is applied to both. I think the problem started when the primer was installed and crushed as seen in the photo. This could have driven the anvil way to far forward just looking for the slightest pressure to fire off the primer. With the impact of the puller the anvil got its excuse and BANG. Do not EVER load a cartridge with a damaged primer. Just my 2 cents BWB