1. Check the length of the front 2 scope base screws. Should be able to remove and look down the front screw hole to see if the scope base screw is contacting the barrel threads. Stick you pinky up into the top recoil lug recess and see if you can feel the hole or screw sticking through the hole for the middle screw. Another easy way to see if the middle screw is contacting the top recoil lug when in battery is to examine the outside face of the lug and look for a drag mark from a long screw.
One could also file the ends of the screws shiny, then sharpie them black, tighten, remove, and look for contact where the screws were sharpied.
2. Fill the front action screw face shiny, sharpie black, tighten, remove, look for shiny spots in the sharpie that would indicate contact where it shouldn't be.
I've recently experienced these troubles on non-mausers. I didn't think there was any way those issues could be MY culprit, until nothing else made sense.
