mauserand9mm,
"The parallax isn't always correct for the distance it's supposed to be set for. Even with adjustable parallax scopes the distance setting isn't accurate."
That's pretty common knowledge among experienced shooters--and it's due partly to the variations in manufacturing, and also to variable magnification scopes. It's also less well-known that parallax can vary from day to day, due to air density.
Which is why for the absolute minimum aiming error due to parallax, you have to compensate, which can be done in several ways:
1) Centering your eye behind the scope. This is what KC is trying to accomplish, but its most precisely done by moving your aiming eye closer or farther from the scope than the distance allowing the full field-of-view. This results in part of the FOV being blacked out, which is due to seeing only through the exit pupil. If you center this smaller FOV, and also the reticle, when aiming, there is no parallax, because your eye is aligned with the center of the scope.
2) Adjusting the parallax of the scope. This is easily done with either an adjustable objective lens (AO), or more commonly these days, a knob located on the left side of the scope.
3) Focusing the scope. Parallax can be affected both by the focus on the front of or side of the scope, but also from the two typical adjustments of the rear focus, either screwing the entire bell in or out, or (on many more recent scopes) the "quick-focus" ring on back of the rear bell. This typically doesn't affect parallax as much as 1 & 2, but can definitely help.
4) Variable scopes complicate things, because the change in magnification often results in changes in parallax, which are exaggerated in higher-X scopes. From about 10x down, this isn't much--but above 10x can be--which is why most scopes over 10x feature some sort of parallax adjustment. (In a worst-case example, I once tested a 5-15x scope made by a major "alpha" Eurupean company--which did NOT have any parallax adjustment. On 15x it had around a foot of parallax at 400 yards. I doubt many shooters have seen one, since it did not last long.)
Most scopes up to 10x (including variables) are set at the factory to be parallax-free at a certain range. If they do not have an AO or side-focus, the typical range they're set for is 100-200 yards. If they show considerable parallax at those ranges, then the parallax setting was off at the factory, which is not unknown--which is exactly why I asked AC what kind of scope was the problem.
The model he has should NOT show significant parallax at the ranges he's shooting.
