Some time back a fellow here on this forum sent me 4 drops of stainless steel through-hardened and normalized to around 36RC (I think) which is (I think) nearabout what a sizing die is hardened to. I will have to go look again but they were two each of 2 alloys of SS...... He sent them to me to make sizing dies from...one of the steels machines OK for me with my small Bridgeport mill and G4003G lathe, the other just shrugs my tooling off.
BTST I can quite easily machine out Redding dies using carbide tooling, I buy Redding dies and re-cut them at will in the making of "ring" and "small base" and other two-piece sizing dies. Other brands simply don't cut and some brands are case-hardened so thinly that while I _can_ cut them I end up going right thru the casing and bogging my tooling down like a Travelall in a frost boil, down to the diff.
I cut "dry" or with squirty-type oil, I believe that to effectively machine many of these mid-range hardened steel alloys one need be an actual machinist using actual modern machining tools using coolants and feed/speeds effectively, not hobbyist or "gunsmith" grade stuff. ((Which incidentally was state-of-the-art not so many years ago
))
I've so far got notes describing re-machining RCBS, Forster, LE Wilson, Redding, Lee and Hornady sizing dies and seaters. I've had success with Redding.
I've also used Newlon and PTG die blanks.
Also "Carbide Tooling" is a bitofa' catchall for tooling ranging from "completely useless, cuts poorly and work-hardens worse than HSS" to "Holee KuhRAPP! This is WIKKID!"
Generally speaking solid, ground carbide tooling can allow me to do some machining operations normally held to be beyond the ken of hobby equipment. And when using carbide insert tooling thicker holders are better. Vibration and chatter kill carbide dead.
I've got some very effective sizing dies that were ground off by bellying up to a carborundum wheel.
The idea that a sizing die should touch the shell holder is ludicrous. Almost as stupid as one press being "straighter" than another.
