This question is the 'Black Hole' of Buck knife steel. My answer is who knows. Even the Camillus factory guys won't put a stamp on one steel or another.
I would hedge all bets an say everyone above is about right. If I ever get around to writing a history on the 301 and 303 I guess I will have to try and pin this question down tight. Right now if you say 440A/C pre 85, 425M 86 thru 92 ish, and 420HC after that I will keep silent.......BUT remember some Cami made Buck stamped models came out even up into the late 90's so what heck were they. I do not have all the answers, I hope to interview a Camillus person soon and I will ask him for a clue... I will say this, knives made late by Camillus had Cami steel not Buck steel. IE examples; 307s, Barlows, big trappers, congress etc.
These were mainly the SMKWs special order models.
I do know the old long pulls seldom show rust. The 425M knives hold a slightly better edge than the old ones and the 420HC's fit in the 'current' B'knives capabilities world, hows that for a broad statement.
ch/300