August September 2021 Machinist Workshop Magazine has a 5 page well illustrated article on making dies. It’s on the shelf at Barnes and Noble now. Worth a read even if you only plan to make die parts like expander plugs.

Boats

It was a good article but my particular interest expander plugs and neck size bushings not covered. He buys his expander plugs & machines the body’s. 

Way I make expanders, Rough it out & leave a tenon one end to chuck the plug in the 4 jaw. Thread & Knurl first then reduce the plug end to what I expect to want. I can turn to about a thousandth what I can’t do is predict exactly what size Plug I will want. Wall thickness spring back bullet pull etc is a considerable variable.

With the tenon one end I can mount the plug in the die body and run some test cartridge cases  getting the amount of expansion right by re chucking & reducing.  Go too far gives me a blank for a smaller bullet  cartridge. Then part off the tenon.

Free machining steel expander works OK in larger calibers & last longer than you would expect.. Size right either run it or use the dims to order a hard plug from CH4D

Neck bushings it’s also trial and error. I set up with rod that’s longer than needed. Turn to OD bore to expected size & part off. Not right the rod stock is already chucked and easy to have another go at it.

Boats