Aren't they a straight-wall for the body?
I wonder if you could just cut down a WSM die for a sizer. In any case, sounds like a massive marketing fail from the cartridge designers. It kills me how many folks think they'll make a killing selling brass to the masses of customers as a sole-source (or nearly so), when that very monopoly is the reason they stagnate; if you even dangle the possibility of them doing it themselves 'open source' style, you make even more money selling equipment to do so before making the same original money on ammo/brass sales when most folks realize it isn't worth the trouble over factory brass
TCB