[dmazur]

I use Hornady dies for .243 Winchester, because Dillon doesn't make dies for that caliber. They work fine.

Some pistol dies have kind of a "squared off mouth" and this can cause trouble with a progressive press and straight-wall cartridges. When used with a single stage press, the operator aligns the case and the squared edge isn't a problem

The Dillon dies have a deliberately radiused mouth to help align the cases as they all go up together. Basically, too many things for your fingers to try to align...so the dies are designed to make things work better.

However, Dillon isn't the only manufacturer to offer dies with radiused mouths.

Dillon dies may have other features, such as easy disassembly for cleaning without removing the die from the toolhead, but these aren't necessary for them to work on a progressive press. Just really handy.

Dillon's QC is pretty good, too.

As to the question about caliber conversion, yes, your list is correct. Except for the primer mechanism. The parts are included with the press, so you don't have to buy anything. But you may still have to swap the parts, if you are going from a cartridge that uses large to one that uses small, or small to large.