Miller, it could be possible that the thin case isn't hardened in a heat treating sense, but might skate a file. A thin oxide layer, not related to case colors, can be hard on cutting tool edges, and some folks like to remove it first before machining a piece. In any event, an abrasion resistant surface may meet the goal of wear resistance of the working parts of a gun.
I think if temps are actually 1200* to 1250*, that'll likely be less than critical temp for any steel. I think Doc Gaddy's drop and hold at a lower temp keeps some predictability in the process. The other strategy of letting the crucible cool for five, or whatever time, minutes before quenching the contents seems more related to the 'art' of case coloring.
