John, Case color is actually a byproduct of the suface hardening process. Many machine parts including doublegun frames are case hardened and what that means is the the surface of the frame is made hard generally about .010-.015 deep while the subsurface of the frame remains soft as in the steels natural state. If frames were through hardened they would not be able to withstand the repeated pounding they take upon firing without suffering failures ie:cracking. In answer to your question if a frame has no visible case color left on it that does not mean it has become soft. A frame would have to be put in a furnace and brought up to temp to anneal it. That would be the only way to make a frame completley soft. Problem is that if this is done distortion of the frame may occur. Parts can be case hardened without achieving case color also. A perfect example of this is to heat a part made from Cold Rolled Steel cherry red and then dip it into a cyanide powder. The surface will harden to about .015 deep.
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"Much care is bestowed to make it what the Sportsman needs-a good gun"-Charles Parker
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