Last year Connecticut Shotgun let one of the shooting TV shows do a segment on how they get their case colors. Kind of a generic presentation with not a whole lot of info, but the camera clearly showed the oven set to 1331*. I don't know if that had any significance, but if the parts were quenched at that temp, there would not likely be any ability to harden the surface or otherwise. The demo was on an over under receiver and it seemed to come out with the right look.