I no longer stock pile ammo.
I had to pull about 250 rounds years ago. Most was LC brass.
The Dillon RL-450 shell plate pushed the shoulder back on fl sizing a different amount at each station.
The worst station was .014" This caused case head separations. Every 4th round was bad.
This and with the necks coming off, i was afraid to shoot the M16A1 carbine, when it became a high priced collectors item. Sold it.
Hope you get it figured out. Wheres all the metallurgist when we need one.