Vapodog and Noway: Thanks again. Maybe I' m too idealistic expecting to not have to re-sight a rifle before every shooting session, but I have guns that never change zero (as do my friends). Plus, even if I did have the luxury of sighting in before a hunt (which usually impractical and noisy at hunting camp), it still doesn' t explain why the rifle changes during the same day. I have a friend who' s a police sniper, and he says he' d chuck any rifle that did what mine was doing. (His duty weapon is nothing fancy, either; just a heavy barreled .308 M700).

Larry338: I' d also pondered how I rested the rifle (great minds think alike, right?), but I kinda doubt it for the following reason: I often alternate rifles when to let the barrels cool. I' ll shoot one shot out of the .300, then lay it aside while shooting something else, then repeat for a five-shot group out of both rifles. (I know that' s not proper benchrest procedure, but it eases the boredom of waiting for a barrel to cool.) If anything, such a practice would lead to large groups, but it still shoots tight groups. But later in the day (no temp change) or after I' ve zeroed for a different distance, it' ll shoot several inches off.

Right now, I' d rather have a 2 MOA rifle that holds zero day in and day out that my sub MOA rifle with a wandering sero.

Thanks again for all of your input. A mechanic buddy has a great saying: " It' s alway' s something simple." When I find the answer, I' ll probably kick myself.