I then purchased a new PaceSetter 3-Die Set in .303 British and a spare expander as the old expander seemed a little out of true.
The 303 mystery deepens!. I've received the new dies and I've got a Mica Case neck lubricator. I've just resized three cases lubed and with the mica inside the neck and the fourth has had the neck ripped off exactly as before. The broken bit hasent got stuck inside the die this time, thanks goodness! but I'm now a complete loss as to what to do. Beginning to think its a bad batch of brass.
I have attached a photograph of the ripped case and the neck stuck on the expander.

Previous to this I have used the original die set to prepare approx. 300 rounds of ammunition with no issues. The brass has the same headstamp.
I have also emailed Lee for help
Please help it’s very frustrating.
Norman