After re-reading most everything, I am of the opinion those cases are most likely soft in the head area through improper hardening andannealing, ie: annealed too far or not hardened enough.
I do not call dropping primers - "popped" - it is actually quite serious & not to be taken lightly - exceeding the elasticity of the case head happens just before all hell breaks loose.
It requires enormous pressure.
-------------------- Daryl
"a gun without hammers is like a Spaniel without ears" King George V