0.920" is the current maximum SAAMI headspace for 45 Auto/ACP guns, but I don't know if it has always been that.
Ordnance blueprints I have (regardless of vintage, 1940 to 1990's) show 0.925" of maximum "breeching space" for Gov't Issue 1911's.
Can't asnswer any of your other questions.
Regardless
When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]
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