Hi BR! It isn't fastened at the rear.  It just sits on hardened set screws, under tension from the big leaf spring under the scope in your picture.  One can pull up on the rear of the scope, rotate it 90 degrees and it comes off.  I keep a bolt that has a Rice sight on it to use the rifle without the scope, which now a days never happens cause I can't see without a scope anymore. Return to zero seems to be pretty good if you make sure those set screws go back to the same place by lightly thumping the mount at the rear ring.

---