I took the scope off my FX 400 yesterday to check the barrel screws. The screw all the way at the rear of the block on top was loose. It does not hold the barrel. What is it for? I tightened it down. Thanks.
I think Hummer 57 is right. It is a very short screw. I can see an o ring under it. I will add some blue loc tite and screw it in just below flush. Thanks