After reading ToggleTops post I seemed to remember that I had seen a pistol with almost the same finish in the milled out areas. After some thought the pistol turned out to be a 42 chamber dated Mauser Banner Commercial. The milled out areas show a definite matte finish, and when viewed under 10X magnification the sandblasting is evident. The milling marks definitely show on this Mauser Banner, but there is also evidence of the sandblasting over the milling marks. Supposedly the Mauser Banners were a good place to use parts that were slightly out of spec for the military, and these parts were simply used on the non-military pistols. I have no explaination for the sandblasting being used on a militry contract pistol, but apparently the practice of sandblasting was in use during this period of manufacture. Thanks for jarring my memory.
I'm not sure when bead blasting came into use, but the US military specifications called for sand blasting before the finish was applied in 1941 for Colt and in 1942 for the other manufacturers. For a brief time Du-Lite blueing was used over the sandblasting before phosphate (Parkerizing) was specified.
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