Thread: Fill length resizing not using expander button.

If you do not use an expander (or a mandrel), then you'll obviously leave the necks undersized. More or less depending on the brand of the die and thickness of the brass.

You are not working the neck less and doing anything to promote greater brass life over the entire reloading cycle vs using an expander, because the bullet itself is going to act like a mandrel and open the neck up to final diameter when seated (and it's larger than the expander anyway). Then the entire case neck is going to fireform out to a larger diameter again when you pull the trigger anyway. You're just removing an intermediate step.

If you don't poke the shank of the projectile all the way down through the neck during seating, it's going to be very visually obvious because the step between the remaining undersized neck and top portion that's been expanded by the bullet is going to be much bigger vs having used an expander.

Honestly, all this seems to accomplish is massively increasing neck tension and increasing the force required for seating (potentially deforming the bullet where the stem contacts it) for no good reason.