Blue to Phosphate

When Ordnance ordered the change from blue to phosphate on the 1911A1 pistol, Remington Rand had a supply of receivers already finished in Du-Lite blue. Ordnance allowed Remington Rand to continue finishing in Du-Lite to use up these receivers before changing to phosphate to avoid mixed finishes.

At Colt it appears that Colt shut down the bluing facilities one night, and started finishing in phosphate the next day. The blued Colt 1911A1 is found into the mid 734,000 range, and after that they appear in phosphate. Any blued Colt after the mid 734,000 serial number has more than likely been changed from phosphate to blue, as this is a way for unscrupulous sellers to boost the value.

Ordnance did allow Colt to continue using some blued small parts until the supply was exhausted. This is a fairly early phosphate pistol which has blue grip screw bushings, grip screws, hammer and sear pins, and magazine catch lock. At this time some of the large parts like the hammer, slide stop, trigger, safety lock, and grip safety have a darker appearance, but this was due to these parts being heat treated, and coming out of the phosphate finish with a darker appearance.

https://www.milsurps.com/images/impo...7/nbrjt0-1.jpg