Not missing that at all. I've made my own tooling before, but it usually isn't worth the effort when only making a few parts.
. Learn how to heat treat and temper steel, and you’ll have to worry about your final dimensions once.
I know quite a bit about this. I usually make my custom cutting tools out of T-15. Lasts longer than O-1. I'd worry about deflection and distortion when machining out brass that is this thin, and of course it's not anywhere near cost effective as just buying ready made. Those poor suckers who have firearms with obsolete cartriges are kind of over the barrel if they want ammo aren't they?
Yes, they are. I know of at least two guys (one in Cody, WY and another around Rapid City, SD) who make brass for obsolete cartridges. They charge pretty well for their products, which are at the very least visually quite pleasing. They’re doing as I mentioned - machining them out of 260 bar stock. As you can guess, the cost of the end product causes your breath to escape out of you as tho you were just punched in the gut. Still, as you say, it’s the only option for those old timey rifles and pistols.
re: T-15 vs. O-1/A-2/etc: If I’m cutting something like brass, I don’t need really good HSS like a T-15. O-1 is just so cheap compared to good HSS...
And mind you, I like T-15, or Rex-95. Lately, I’ve been playing with inserted HSS tooling from A. Warner Co. in PA. Neat idea - combine the flexibility of HSS with the speed of insert tooling. Really cool idea. I like their threading tool because it is external on one end, internal on the other.