CSMC/Standard Mfg does it's own color case hardening in their facility in New Britain. When he first started mfg the AH Fox in 91, he used Turnbull for CCH.
He set up his own case hardening about 95 at his orig plant in NewBritain and has done his own ever since. Fox, Win/CSMC21, O/Us, RBL, Parker special order for Remington, pistols, ect. Bone & charcoal.