My first go at reloading for .303 Brit

[Parashooter]

Dragging that mandrill back up through the case has to do a lot of stretching of the case.

Imagine what it would do to the mandrill.

Attachment 26327

On the other hand, the mandrel of the Lee collet die is highly polished - and since the brass springs away from it once the collet is released, there's no stretching involved. With conventional expander/sizer dies, there is no mandrel - just an "expander". If kept clean and case neck interiors appropriately lubed they don't stretch cases axially either - although their job is to stretch the neck radially for a good fit on the bullet.