Slightly expands the case neck so that the bullet can be seated easily.
- Straight wall cases require an extra die to expand the case mouth. The case mouth needs to be slightly flared to allow seating of the bullet.
- This die is usually found as the second die in a set for straight walled cases.
- Bottleneck cases get "expanded" as the case is drawn over the expander ball while being removed from the resizing die.