foxtrot
Most fixed parallax scopes are set at 100 or 150 yards. Many rimfire scopes are set at 50 yards. If you shoot at a range that is closer or farther than your parallex free range, you will have some error. This error is visible if you fix your rifle on steady rest (like a shooting bags) and move your head side to side while focusing on the target. You will notice your crosshairs seem to wiggle or move around. By doing this test you can see how much error you are getting. For big game hunting, fixed parallax scopes usually don't pose a problem because of the larger target size. As a fixed parallax scope's power increases or if the objective lens gets larger, the parallax error grows. A 32mm objective, fixed 4x power scope will have very little parallax error at varied ranges. A 12 power scope with a 50mm objective will have a larger error at varied ranges. There is a way you can "cheat" the parallax error on a fixed parallax scope. This is done by moving your head back outside the normal eye relief zone until you see a black halo around the picture. Make sure this black halo has equal thickness the entire way around the sight picture and then touch the trigger.
conclusion:For precise benchrest and varmint shooting at ranges greater than 200 yards, I recommend using an adjustable parallax scope to ajust out the error. You will definitely see your group sizes shrink when the parallax error is diminished.
Not to sound like a salesman, but the Nikon Buckmasters 18power scope with target turrets is a pretty slick scope without breaking the bank. Perhaps I'm biased because I own one.
Happy shooting!