Parallax adjustment is something that many shooters do not concern themselves with until they begin to see inconsistencies in precision long range applications, but understanding parallax is something that all shooters will benefit from. Regardless of short-range or long-range shooting, hunting or target shooting, parallax makes a great impact on consistency in accurate shooting. Those who are not willing to admit their shortcomings as a marksman are often victims of ignorance to the effects of parallax or how to mitigate it.
What is Parallax
Parallax can be difficult to explain, and sometimes even more difficult to understand. The basic concept of parallax in the context of rifle shooting is the difference in alignment between the target, the method of aiming, and the shooter’s eye.
The easiest way to understand how parallax works is to place your finger between the eye and something on the screen you are reading this on, masking that image with your finger. Now move your head from side to side and notice how when you change the alignment of your eye to the reticle (your finger in this case) your sight picture is completely changed.
How Does This Affect Shooting
Those who were taught to shoot an M16 by the military would have learned that they should place their nose on the charging handle in an effort to achieve the exact same sight picture every time. You may or may not have realized that this was preventing the effects of parallax to increase accuracy. Many rifle stocks have cheek risers and other tools built into them to help the shooter achieve a consistent cheek-to-stock weld, and therefore mitigating effects of parallax.
Many optics are advertised as parallax free. While this is a bit of a white lie, red dots and holographic sights do help to mitigate the effects of parallax to an extent, but when shooting longer ranges or when shooting from less than optimal positions the effects can be observed. The easiest way to prove this to yourself would be to lock down a rifle in a bench rest with the red dot or holographic reticle on a target and move your head around like in our previous exercise and witness the reticle move off of target, even if ever so slightly.
We stated earlier that we are concerned about precision long range shooting, and we will not be able to rely upon technology found in red dots or holographic optics to mitigate our parallax effects in this application. The reticles found in scopes will be susceptible to the effects of parallax, and the shooter must learn to maintain a consistent cheek-to-stock weld to mitigate them. However, many scopes designed for precision rifle shooting do have technology built into them to give us an advantage.
Parallax Effects in Different Scopes
In precision long range shooting, there are basically two types of optics used; fixed zoom, and variable zoom optics. With fixed zoom scopes, there is absolutely a parallax effect that needs to be mitigated, but it is constant throughout the range of potential distances you might be shooting. Think of parallax effect on a fixed magnification scope in measurements of MOA or Mils where the margin of error can be determined as an angle from the scope to the target. This will usually be rectified by perfecting a consistent cheek-to-stock weld.
Variable zoom scopes do not have the same luxury as you adjust the level of magnification in the scope. As you adjust magnification, parallax effect will continue to change. If you lock your scoped rifle in the bench rest again and adjust the magnification you will see that the crosshairs will wander about the target a bit. This can be mitigated if your scope has the proper adjustment built into it.
I want you to take you back to the exercise we did with the finger over your screen. Now put your finger right on the screen and move your head from side to side; you will obviously find that your finger will continue to cover the “target.” Scopes designed for precision shooting will have an additional adjustment to correct parallax.
While the parallax adjustment can vary a bit depending on the manufacture, the most common adjustment method for parallax correction is found on the left side of the scope in the form of a knob. This knob is sometimes referred to as a focus adjustment, and that can be a good thing or a bad thing depending on your thought process. On one hand it dumbs down the actual purpose of the knob in a way that causes the shooter to inadvertently use the adjustment correctly, and on the other hand it encourages ignorance instead of labeling it for its true purpose.
This knob will cause the picture in the scope to become clearer when it is adjusted to the proper setting, but that is only a positive side-effect of making the correct adjustment. What the parallax/focus adjustment attempts to do is simulate the same affect as when you stuck your finger right on the screen. While this is not completely fool proof, it will decrease the effect parallax has on your sight picture in a quality manufactured scope.
When you have the parallax adjustment on the proper setting, and you use a consistent cheek-to-stock weld you will inevitably find yourself much more consistent and accurate in your long-range shooting.
Are You an Expert Yet?
The way that parallax effects shot placement is a real and measurable metric, but it can be quite challenging for many people to grasp how it actually works. While we have possibly over-simplified the concept in this article, the ways we mitigate parallax effects on precision shooting are relatively simple and can be both learned and improved through equipment. As with all types of shooting, the best equipment in the world is no substitute for training so I encourage all of you to get to the range and work on your shooting position and cheek-to-stock weld. Of course, if you don’t have a scope with parallax adjustment, I recommend you try one out and give yourself the extra advantage.