The intro in the Scrap Yard Knife site says that Dan really liked the shock taking qualities of S-7. I think S-7 is the basis for SR-77. Dan's 40 hour heat treatment transforms the S-7 into SR-77. At least that is what I get from their own web site. All I know for sure is it is tough. I have pounded the Dog Father and the S6 through knotted, dry, hard liveoak with no damage or failures. I destroyed the edge on a Condor 420HC doing much less. And 420HC is not all that bad a steel for most uses.