Hey 45B20,
Yes I'm aware of the difference between forging and heat treatment. The control and monitoring of the heat to forge temperature is a vitally important quality control step in the manufacture of a forged part, since the integrity of the forging hangs on this operation being performed properly. The hot working (forging) operation is carried out in the austenitic temperature range for ferritic steels, where plastic deformation is performed above the recrystallization temperature. As the hot working (forging) temperature is increased, beyond the optimum range for the particular type of steel, severe crystal grain growth becomes a serious problem, affecting the mechanical properties of the finished forging. This condition is called "Overheating" and requires additional heat treatment steps to restore the desired mechanical properties of the forging. If the hot working temperature is increased further, grain boundary oxidation occurs. This condition is referred to as "Burning" and is irreversible. The mechanical properties of the steel forging are degraded, including ductility, tensile strength, yield strength and toughness. Forgings that are "Burned" during the heat to forge manufacturing process are only fit for the scrap heap. The fatigue strength of the steel is severely reduced too due to increased stress concentration sites, these are created by oxidized crystal grain boundaries at highly stressed surfaces.
Heat treating a "Burned" forging will not reverse the degradation of mechanical properties.. Steel is heat treated to alter it's physical and mechanical properties. Heat treatment is performed by subjecting the steel (or steel forging) to controlled heating and cooling. Heat treatment of forgings plays an important role in developing desired properties such as increasing toughness, strength, relieve internal stresses, etc.

The "Low Serial Number" S.A. and R.I.A. forgings were not subjected to close monitoring of the heat to forge temperature (eye balling color of forging was the norm!) and of course varied from operator to operator, time of day, season, etc. so some of the forgings were "Burned" and became brittle and subject to catastrophic failure if subjected to higher than normal forces or loads (sharp blows, cartridge failure, overloads, etc). The "High Serial Number" S.A. and R.I.A. forgings were subjected to close monitoring of the heat to forge temperature via Pyrometers and thus the material properties of the forged parts were not degraded.

There is no non-destructive test that I know of that will separate the "Burned" forged parts from the properly manufactured ones.

I gave the OP the link to the CMPicon to point out that the receiver was not the only suspect part, but the bolts of that vintage are also suspect.

D.