Bushing Dies vs. the Expander Ball
Here's the difference ...
Shooters that are concerned with precision shooting make their handloads fit their chamber as close as possible, and perfectly resized handloads will NEVER develop headspace separations. Precision handloading helps cases last longer, because it reduces case stretching.
The expander ball can stretch your case slightly longer than your chamber (as reported). This is no problem to some shooters. However, it's far better to make handloads fit perfectly, because it provides the best accuracy.
If your cases are resized too short, they'll chamber and go BANG just fine. But these cases get stretched too much when they're fired. That often makes the brass paper thin, and each shot brings you closer to a headspace separation.
If your cases are sized too long , it can require forcing the bolt closed. You should not be able to "feel" the bolt close on a round - not even a little bit. The precision shooter always wants concentric handloads. When you jam the rounds into the chamber even a little, your concentric handloads become anything but concentric.
Due to the different neck thickness of brass, the expander ball is ideal for basic reloading. It almost always provides your case with a uniform ID, and you don't need to worry about the varying neck thickness of your brass. Occasionally reloaders will turn down the expander ball to compensate for loose bullet tension or neck stretching. However, no amount of case chamfering can fix neck tension problems. If neck tension is too much, it ruins concentricity (case run-out).
The expander ball works because your resizing die first reduces the case too far, then the expander pulls the brass in the "opposite" direction to the perfect case ID. This "extra" working of the brass will harden your case necks far quicker than a bushing type die that only moves the brass directly where it needs to be.
The nice thing about handloading is that almost everyone can participate to the degree they are interested. It's not rocket science, but we can all learn something new in the pursuit of better rifle accuracy.
- Larry