Split case necks - Hornady brass

[biodsl]

Like '52 says, use some spray 1-shot and that gets some lube into the inside of the neck.
The excessive work hardening of the neck area is what I would suspect. I was using rcbs lube on the outside but inside necks were bone dry. Once I made the switch and got some 1-shot on the inside neck, the splits stopped.

Interesting. I ever only used One Shot. I've never had a split neck.