I don't think that it is hard. Sounds to me like the same problem as in the recent burr thread. It just confirms my own experience that 420HC, as it is commonly heat treated, is just plain low grade steel. It sharpens about as well as a rubber tire. You just don't get rid of the burr and even if you do, you use it three times and the edge just rolls over. :barf:
I don't really give a damn that its composition is not so different from 12C27 but in my experience the two don't behave at all alike.
Sorry for the strong words, I have held back on that for a while, since Buck's 420HC seem to have a strong following, but now reading twice what mirrors my experience, I think it's really got to be said. I don't want to tread on anyones toes, and maybe Buck has changed something in their heat treat in the past 10 years, but the two Buck knives in 420HC that I bought about 10 years ago are worse than a Ginsu 2000. Sharpening a blade in S30V is a breeze in comparison.
(Just to point out that this is nothing against Buck in general: My Kaala in S30V with Bos heat treat shows excellent performance steel wise. Couldn't be happier with the steel).