I do not find references to chrome moly experiments at Winchesters leisure, in Hatchers Notebook or his Book of the Garandicon.

Winchester followed the contract exactly, causing many little headaches and did not revise the receiver version from "-2" till 1945. they were not paid to change it, so did not. Same thing on many parts.

Chrome moly is generally in the 4000 steel range.
That steel is not up to the required "WD8000" steel series standards-- (War Dept for WD) after the "diamond change" and not referred to in the earlier mixes at all. I also refer the reader to the Kuhnhausen book and the Pyle book.

Op rods were a mix of two parts and two steels, but no chrome moly. Gas cylinders were a SS blend. All parts had specified steels that were used.
That is fact, and no messing around.

I believe that the long held idea that "CM" was just a reference to a local manufacturer or subcontractor is still substantially correct.

Winchester would NOT experiment, could not experiment or be ALLOWED to experiment with ANYTHING in metal composition outside of specs-- due to the specified contract costs and specific materials being specified in detail.

For Winchester and their reputation to go way out on a limb and say "hey we gotz some time and lets try some new plastic copper nickle wizbang new process to stick in those them there Garands"--- it is ludicrous to consider it in war time, with all the inspectors and Art Tuttle and John Garand so close by.
I can almost guarantee that CM would not refer to any different steel or extra process, secretly done by Winchester, any more than "A" refers to the human posterior.