Lee has for some time been selling a "Universal Case Expander" die, which is anything but. All it does is flare the case mouth.
But the design is clever. A hollow die body with two sliding inserts that are the flaring plugs.
It didn't take long for few folks having a lathe to recognize that proper expander mandrels could be substituted for the Lee plugs. Al Nelson at NOE Molds already has a selection on his web site. Alternative expander mandrels are a good start.
The image below shows tools I made last week to help a friend with reloading the ultra-obsolete Stevens 28-30-120 cartridge for his 115-year-old Stevens 44. Brass is almost unobtainable, and very costly when you do find any. Dies ditto. Since he won't be shooting the old Stevens much, he didn't want to shell out for a pricey set of custom dies. Can't blame him.
He needed his brass full-length sized, and I do happen to have a rare .28-30 set from C4HD. But while they are high quality, the M-die style expander is worse than useless. It actually mutilates that precious brass, and is the wrong size for cast bullets anyway.
What was needed for the long skinny .28-30 case was a long mandrel with a gently tapered lead-in, to maintain concentricity. Easily done on the lathe. The two parts on the left are the mandrel and a spacer to lift it high enough in the Lee die body to get the case under it in the press. The mandrel is custom sized to the exact bullet he is using.
He should have a seater. The three parts on the right are a guide sleeve, a top punch, and another spacer to position them in the die body. Seating depth adjusted by the Lee top screw. Crucial since the .28-30 has no throat at all, just a very steep-tapered leade.
He also should have a neck sizer. In the middle is a button much like those supplied for the Hornady benchrest dies. Used with the same long spacer as the expander.
All the parts except the spacers are 12L14 steel. Since he won't be shooting the Stevens much, this will be fine. I chose 12L14 largely because I had some on hand. 41L40 would be better. Both are available online in 9/16 finished rounds, which fit the bore in the Lee die body and my collet chuck. Less machining that way. The spacers are 4130 tubing. Unnecessary, but easy to find online in 9/16 O.D.