Mitch, You say,
There is also no mention of "7.65 Mauser" in his 1971 work "When They Kill a President."
I just read through Craig's book, When They Kill a President... He does mention a Mauser (below):
Capt. Fritz asked if anyone knew what kind of rifle it
was. Weitzman asked to see it. After a *close* examination (much
longer than Fritz or Day's examination) Weitzman declared that it
was a 7.65 German Mauser. Fritz agreed with him.