Long Range Shooting: Precision Rifle Scopes
Long range shooting scope anatomy
Modern long range scopes (telescopic sights) are made in various sizes, shapes and feature sets.
Depending on your mission they will have differing reticles, weights and adjustments.
The best scopes for our purpose have the following anatomy starting at the front of the scope (the part closest to the muzzle) and working back toward the shooters eye.
- Objective lens
- The objective lens purpose is to transmit light back to the ocular lens, and their diameter is measured in millimeters, e.g. 50mm. The objective lens has no bearing on "magnification" or power of the scope. The larger the objective size, the more ambient light will be introduced into the scope and to your eye.
- Adjustable objective (AO)
- An adjustable objective is often a dial/ring around the objective bell, or a knob on the left side of the turret housing. The function of the AO is to allow you to adjust your scope's parallax to a certain distance, by moving these adjustments until a clear picture is perceived, and/or the marked corresponding incremental yardages are approximated to your target distance. The correct setting of an adjustable objective prevents the apparent movement between the reticle and the target when the shooter moves his head slightly off center of the rifle scope, otherwise known as parallax error.
- Scope tube (barrel or main tube)
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The scope body is a metal (usually aluminum) tube that holds the lenses in place. The tube is also used to attach the scope to the rifle using scope "rings".
The exterior of the scope also contains all of the necessary controls for making adjustments to the lenses. The front of the scope tube widens to accommodate the objective lens, and this flare is known as the objective bell. The rear of the scope widens to house the ocular lens, and this wider portion is known as the ocular bell.
The most common scope tube sizes are 1 inch, 30mm and 34mm. The diameter is measured by the size of the main tube between the adjustment turrets and the objective bell, and the diameter from the turrets to the eyepiece, or magnification ring. The 1 inch scope is usually lighter and a 30/34mm barrel is usually thicker, heavier and the internal diameter of the telescopic sight main tube influences the area light can pass through. Lens elements and other parts can be mounted in, and can control the internal parts for elevation, and the windage adjustment can move. The larger tube allows for greater elevation/windage changes and therefore, it's better suited for long range shooting and hunting.
The internal tube is "purged" and sealed so that rain and moisture won't get in and fog the lenses.
- External adjustment turrets (turret housing, windage and elevation adjustment)
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The three most common adjustments for any rifle scope are windage, elevation and parallax.
The windage turret sits on the side of the scope body, and allows you to adjust the horizontal alignment of your reticle to adjust the point of impact for wind. The elevation turret sits on top of the scope body, and provides vertical adjustment for your reticle to adjust for the bullet drop to the target. Typically windage and elevation adjustments are measured either in MOA (minutes of angle) or MRAD (milliradian) measurements.
The parallax error adjustment turret (also known as the AO) sits on the side of the scope body, and changes the adjustable objective lenses to correct for parallax error.
Zero-stop elevation controls (part of the elevation turret) are a great feature for long range shooters. They can be set to prevent inadvertently dialing the adjustment turret "below" the primary zero. This feature is useful on long-range scopes, because it allows the shooter to physically verify that the elevation turret is dialed all the way down, avoiding confusion regarding the elevation status on two- or multi-revolution elevation turrets.
Reticle illumination controls on the side of the scope body can also be useful for long range hunters in low light. The illumination adjustment control of the reticule regulates the brightness level of the lit parts of the reticles crosshairs. With any illuminated low-light reticle, it is essential that it's brightness can be adjusted. A reticle that is too bright will cause glare in the operator's eye, interfering with the ability to see in low-light conditions. This is because the pupil of the human eye closes quickly upon receiving any source of light. Most illuminated reticles provide adjustable brightness settings, to adjust the reticle precisely to the ambient light.
- Magnification power ring (power adjustment ring, zoom ring)
- Usually located on the smaller ocular lens/eyepiece as a rotatable ring. Turning the power ring changes the magnification setting on the scope. In a variable power scope, this ring allows the shooter to adjust the power between it's ranges. For a long range scope, that may be 5-25x for example. Turning the ring will make the target appear closer or further away, and the magnification setting will be between 5x - 25x times the original size in the scope. A larger magnification leads to a smaller field of view which can be important in long range hunting.
- Eyepiece
- The eyepiece holds the ocular lens. The eyepiece might be adjustable for reticle focus (a diopter) to obtain a sharp picture of the reticle for your eyes. (It should be set for you only), and you should set the eyepiece focus once, when you first set the scope up and not touch it unless your eyesight changes.
- The ocular lens
- The ocular lens magnifies the light from the focal point, and is usually smaller than the objective lens. It focuses the light gathered by the other end of the rifle scope, the objective lens, into the eye of the viewer.
- The "exit pupil"
- Scopes concentrate the light gathered by the objective into a beam, the "exit pupil", whose diameter is the objective diameter divided by the magnifying power.
Get a scope with at least parallax, windage, and elevation adjustments for long range shooting. Some cheaper scopes only have fixed parallax.
