Each rail manufacturer had/has their own code for the various rail sections. For instance Bethlehem may have used 8540 for 85ASCE, 9020 for 90 RA, 9030 for 90RB, etc. I'm away from my references so I can't precisely say what 301 may be, but I would guess that it's 30 lb rail of (maybe) ASCE section.
Ned