Question #3 - 'kind of sort of' an answer.

Using the bayonet lug or bayonet slot as a point of reference is vague, difficult to measure, and creates a lot of variables.

Maybe there is a better way:

IMHO - Better reference points are the straight edge of the front barrel band, the back edge of the bayonet-guard, and the barrel's muzzle-crown.

The distance from the front edge of the forward barrel-band to the back edge of the bayonet's 'barrel-ring' is 2.825".

The distance from the front edge of the forward barrel-band to the muzzle-crown is 3.20".

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