Ok, a factory tech advised a screw tight order of front-middle-rear. Three posters and a gunsmith from Alaska advised a screw tight sequence of front-rear-middle.
I find there is no single, correct way for all M77s. The only thing that seems to be consistient with the M77s I have owned is the middle screw should only be a light snug and front screw extra tight. Otherwise you need to experiment with the sequence.
