2. What is the thumb notch? Is that the little notch cut below the center line of the bolt on the left side? -
Yes
What is it for? -
Clearance for the shooter's thumb, when pushing down a clip-full of ammo, out of it's stripper clip, into the magazine - a wartime speedloading. The clip lower end fits in the eared slot in the leading edge of the rear receiver ring.
BTW - I can see the doors clearly now (to my nursing home)
(Thanks, JK)
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