icdux1, I disagree strongly with your characterization of the "annealment" mark. It is just the opposite of what you state.
The magazines were formed out of stock that was too soft to not be deformed in use after bluing. Therefore, after the magazines were formed and blued, the upper portion was given a bath in liquid cyanide (about 1,450 degrees F. as I recall), then quenched in oil, to harden them, not anneal (soften) them. The liquid cyanide removed the bluing, but left the feed lips hard enough not to deform in use. The line on the magazines caused by the level of the cyanide bath is commonly called a "temper line," not an "annealment" mark.
This process is described in several Colt books. For instance, see Page 205 of Charles W. Clawson's "Colt .45 Government Models" (Commercial Series), Second Edition.