Regarding Buck's 420HC, they've treated it to higher hardness than (seemingly) anyone else. I looked up a doc from it's manufacturer (Latrobe Steel) a short while back, and they spec'd it for mid-50s HRC. This is what Case's Tru-Sharp is hardened up to, mid-50s (Tru=Sharp is actually 420HC). Buck's much-vaunted Paul Bos heat treat method has taken their knives up to around 58 HRC. That helps for their blades, which don't seem to roll or stubbornly hang on to wire edges as much. Case, on the other hand, has some amazingly stubborn wire edges on their blades. I've spent most of my sharpening time & effort on removing the wires on Case knives, when sharpening them.
The earlier advice, about going LIGHT with the pressure, is good advice for this steel. It's very ductile and not very abrasion resistant. This means metal comes off fast, and if you take it too far past the apex, or bear down too hard with pressure, you'll produce a significant burr very fast. While trying to get a feel for sharpening it, I'd avoid ceramic rod hones (like the Sharpmaker) for now. The narrow contact point, when using a triangular or round ceramic rod, will multiply the pressure on the edge in a big way. For this steel, that means it'll roll very easily. If you DO choose to use the Sharpmaker for it, use only the flats of the rods, with very light pressure. Don't use the corners, at least not yet, until you get a good feel for the steel.
Starting with a higher (finer/gentler) grit helps, in terms of regulating how big the burr gets and how fast it forms. You might give some 600+ grit wet/dry sandpaper a try, on hard flat backing (like glass), with an edge-leading stroke (edge-trailing will produce a burr easily, especially if pressure is heavy). Again, at very LIGHT pressure. The sandpaper will pretty much mandate going light anyway, as you'll cut/tear the paper if pressure is too heavy.
