Rob,
For clarity for all readers, a reamer only cuts on the end. The o.d. is ground like a pin, with chip gullets and there is some relief to control the margins that contact the o.d.. However, only the end cuts as it advances into the part. The end has each flute with a relieved cutting edge.
Casehardened steel has a fairly thin very hard surface followed by a larger gradient of hardness back to the base metal hardness. Still, as the reamer comes into this thin layer, it has to cut it. This layer is hard enough to dull the reamer even though it's thin.
CZ,
As I said, I've not put a new pin in a gun, just mechanical devices and tools. But, I have hardened a good bit of things. I've used Rockwell testers as well has files and punches. For a hingepin, it would seem that there's no such thing as too hard. But rather than use a martinsitic steel (thru hardening), I'd think about a casehardenable steel to facilitate later recasing of the frame.
