When selecting a rifle scope, there are several features that should be considered. Often times, the type of hunting that you will be doing most will dictate some of those features. The following general recommendations will provide a good selection guide for scopes.
When considering magnification keep in mind that as the magnification is increased the field of view decreases. Often times lower magnification is better. Target acquisition is much quicker due to the larger field of view. That is very important when hunting dangerous game. In that scenario a range of about 1-5 power would be most advantageous. At the other end of the spectrum is long range hunting. Antelope, mule deer, elk, sheep, and prairie dogs will fall into this category. The upper end of the magnification range can easily reach 14, 20 or even 25 power for these applications. As the upper end of the magnification range goes up so does the lower end. A 4.5 to 14 power would be a good choice for the person who has one rifle but wants to use it in a variety of situations. Generally speaking though most hunters have several rifle calibers and matching scopes that are used for different hunts. A typical range that seems to be very popular is a magnification range of 3 to 9 power. You do not need any more magnification particularly if the range that you will be shooting is most frequently under 150 yards.
The most common rifle scope center tube diameters is either 1 inch or 30mm. The larger diameter tubes provides more elevation and windage adjustment range, are stronger but somewhat heavier, and are typically found on the higher priced rifle scopes. Be sure that you purchase mounting rings that match the tube diameter of the scope.
Most scopes under 10 power magnification are preset at the factory to be parallax free at a certain distance, typically 100 yards for rifle scopes and 50 yards for shotgun or handgun scopes. When a scopes magnification range extends beyond 10 power then the scope will be fitted with a parallax adjustment, either a knob opposite the windage turret or an adjustable objective bell, allowing the user to adjust out the parallax error for different range distances out to infinity. To determine if parallax error is present, move your head side to side to see if the target stays on the point of aim- if so then parallax is not present. If the target moves off the point of aim then a parallax adjustment needs to be made.
The function of the reticle (cross hairs) is to simply define a reference point to the point of bullet impact at some established distance downfield. Probably the most common reticle is a duplex reticle that is basically nothing more than cross hairs. There are of course variations by manufacturer. Many times there may be several different types of reticles available. The most popular reticle due to its designs have evolved over the years to assist with typical issues the average person experiences with vision problems. A very versatile reticle is the mil-dot reticle. It provides ranging capabilities, bullet drop compensation, cross wind compensation as well as the capability to lead a moving target. The Mil-dot reticle is not cartridge dependent which means it works with any bullet weight, any velocity, at any elevation. See the RCS Optics article on mil-dot reticles for more information. Most manufacturers also have special reticles that assist with establishing a hold over value for bullet drop compensation when shooting longer distances. These reticles are typically cartridge specific. A discussion on reticles is not complete without talking about the focal plane configuration of the rifle scope. There are two focal planes in any rifle scope, aptly named the first focal plane (FFP) and the second focal plane (SFP). Reticles in the FFP will increase or decrease in size as the magnification range is changed. The benefit of this is that the angular measurements of mils or moa will remain constant throughout the full range of magnification. The downside is that as the magnification is increased the reticle can obscure the target. The second focal plane reticle will remain constant size throughout the magnification range however ranging must usually be accomplished at maximum magnification.
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