Happy Thanksgiving !
The material is 12L14 carbon steel as it produces a great surface finishes and rust blues very well.
I made a form cutter out of a straight flute HSS keyway endmill with my surface grinder. Using a radius dressed wheel with spin fixture. It cuts pretty good as a "flapper". I'd rather have a helical carbide form tool, but for now the home made form tool works well.
The variable flute 1/2" & 1/4" carbide mills are from Online Carbide and they eat steel and last well dry cutting. My mill doesn't have flood coolant.
These are the swivel of choice for most of the rifles I build.
