I only got to play with 1 in 19C27 so far (waiting on the Goko's
) and that was here for a major repair. I didn't mean to indicate that it doesn't do well with a J Nat, just that the stones perform differently on different steels/HT/etc. I have found AS LOVES J nat stones for a finisher and R2 is another powder steel, so very fine grain structure as well like AS and carbon steels. I know AEB-L and G3 are very fine grained steels, not sure about the grain size on 19C27; I though I read somewhere a while ago that the grain was a bit coarser with larger carbides in it, but that could have been another steel they were referring to. Of course, the heat treating temps, cycles, quench cycle, etc play a BIG role in how the steel performs, grain/carbide size, etc. I think 154-CM has much larger grain size than the CPM154 powder steel, IIRC I think it was D2 that has some big carbides in it as well?
I was trying to stress the fact that some stones tend to "like" different knives/steels. Many of the finer grained steels seem to do better with higher finishes, where steels with bigger grains/carbides may do better with coarser steels? Something about carbide fall out or something like that? This is going back several years, so I may not be fully correct; it was something to do with sharpening D2 IIRC.