When a reliable rifle starts acting weird, and all the screws are tight, the very first thing I suspect is the scope, because it's almost always the source of the problem.
Especially if it's a variable-magnification scope, not as likely if it's a fixed-magnification scope.
Anything that can move easily when you want it to move, can (and well may) move when you don't want it to move. That's a simple, unavoidable mechanical
fact.
My hunting days are all behind me now � in those fondly remembered old days, I learned never to trust a variable scope on a hunting rifle. My field tests showed how unreliable variables can be, and that it was impossible to predict which ones were most likely to fail in the field. Some of the chintziest X-brand imports were more dependable �
when they were tested � than the most respected big-name brands (which often failed when brand-new).
The optics were usually (but not always!) first-rate. The mechanics of the innards varied all over the place �
some times including soft-aluminum screws, for Pete's sake!
Fixed-power scopes can fail, too, of course � but they're not nearly so prone to mystifying failures as variables.
