Happydog,
Welcome to the Handi world and especially the 38-55's. I have little actual "shooting" time with mine, since it's been involved in a LONG,SLOW, project of mine, but from my experience and what I read of others, they seem to prefer the milder loads.
If your has been rifled differently, that might not still be the case.
I still shoot only BP loads from mine so far, with Chey-Cast 20-1 .379-.380, 235gr bullets.