David Weaver
I had one of those for a knight plane. They may have been variable, as mine was definitely very hard, but a little crumbly. If i'd have kept it, i'd have probably removed it a little just to see if it was a problem of over hardness.

I have to be honest, in not sure that I ever tempered the shooting plane iron that I made, and it works fine. It's too hard to maintain on the washita, though. I would guess it's hardness at 64 or so given my experience with various natural stones (which do a good job of infusing hardness if you have enough different types. )