Selecting a correct scope for a particular application mostly requires common sense. For the time being, I will leave out price range and optical quality. For the most part, I will concentrate on the configuration only: magnification range, objective lens diameter, etc.
Here is the common sense part: if most of the time you plan to shoot at very small targets very far away, you need a rather large scope with high magnification. Here is another common sense argument: if you do not expect to run into these long shots with any regularity, you need an “allrounder” scope of some sort.
Most people tend to overscope their rifles, by that I mean that they pick scopes too large in size and too high in magnification for their usage. As a matter of fact, there are not all that many applicaitons that require very high magnification. I often run into an argument that “if faced with such a shot once in a blue moon, it is better to have all that magnification available”. While sounding good on the surface, the truth is that most scopes that give you high magnification are not well suited for anything else. On the other hand, there are quite a few all-round configurations that allow you to take those long shots in considerable comfort. I suppose, what I am trying to say here in such a round-about way is very simple: when in doubt, err on the side of more conservative configurations. Besides, think of it this way: an object that is 300 yards from you, when viewed through 6x magnification appears to be about the same size as an object at 50 yards looks to the naked eye. The implication is that for most reasonable shots, 6x is more than enough and often less is more.
The most common configurations for big game hunting rifles are “mid-range” scopes such as 3-9×40 and 2.5-10×40, and for good reason. These are fairly easy scopes to build with the low magnification offering enough field of view for close up shots and high magnification being sufficient to clearly aim at a deer-sized animal pretty far out. Definitely further than most people have any business shooting at an animal. Here, it is important to keep in mind that a hunting scope is not an observation device. That is what binoculars and spotters are for. A riflescope is there to allow you to clearly see the target and aim at it; being able to resolve every little detail of the target is not necessary for a weapon sight (although it does not hurt if other properties are not sacrificed). Additionally, most scopes of this configuration are fairly light and can be mounted sufficiently low to not upset the balance of the rifle.
Things change of course once the application becomes a little less general. Some hunting is done high up in the mountains where very light rifles are often preferred (of course some people prefer very light rifles for all big game hunting). In those situations, 3-9×40 or similar is still a very good configuration to go with, but it is worthwhile to find a fairly light scope so configured. Some 3-9×40 scopes are distinctly lighter than others.
Alternatively, you could go with a “tweener” scope of some sort for a mountain rifle. Tweener scopes are 2-7×32 and similar designs. They give up a little magnification compared to 3-9×40, but are lighter and offer wider field of view at the low end. Because of this wider field of view, tweener scopes are also well suited for hunting in densely forested areas where long shots are not typical.
On the other hand, if most shots you take will be pretty long (western plains game hunting, for example), you might want a touch more magnification than a typical 3-9×40 scope provides. However, you still do not want to sacrifice too much field of view. For this, I’d be looking at scopes of following configurations: 4-12×42, 3-15×42, 4-16×42, etc.
For the sake of brevity here are some configuration suggestions in a tabular form. I included both variable and fixed power scopes (this is by no means exhaustive):
Application |
Typical usage |
Riflescope configuration suggestions |
Allround big game hunting rifle |
shooting at deer-size game at close to moderate ranges (50 to 300 yards) |
3-9×40, 2.5-10×40, 2-10×42, 4×32, 6×36 or 6×42
|
High altitude hunting/light rifle applications |
same as above except you are more winded when you take the shot |
1.5-8×32, 2-8×32, 6×36 or 4×32 |
Brush Hunting |
mostly close range shots in wooded areas |
1-4×24,
1.5-8×32, 1-6×24, 2.5×20 |
DGR (Dangerous Game Rifle) |
you are after the largest and most dangerous game that might try to eat or trample you |
1-4×24, 1-6×24, 2.5×20, Refelx Sights, iron sights |
Open Plains Hunting |
sometimes you just can’t get any closer, so you may have to take a 400yard shot, while anything less than 100yards is not likely |
3-12×42, 4-16×42, 3-15×42, 4-16×50 |
Ultra-low Light Use |
Most of your shots will not be particularly long, but visibility is likely to be atrocious |
2.5-10×56, 3-12×56, 7×56 or 8×56 |
Tactical Carbine/SHTF (typically AR-15 with 16″ barrel) |
Anything from clearing buildings to mid-range engagement |
1-4×24,
1-6×24, 1-8×24 |
Walking Varminter |
You plan to mount this scope onto a rifle that you need to be able to carry with you. You mostly plan to shoot at coyote-size targets, or a little smaller and the distances can be pretty significant |
4-16×40, 2.5-16×42, 3-15×42, 3-18×44 |
Long-range Varminter |
This scope is likely to be mounted on a heavy-barrel rifle to shoot at prairie dogs or similarly small targets that are never that close |
10-50×60, 6-24×50, 8-32×56 |
Target Shooting |
You are trying to print the smallest possible groups out on the range with a dedicated heavy barrel rifle |
6-24×50, 8-32×56, 10-50×60, 15-60×52, 20×42 or 24×42 or 36×42 |
Mid to Long Range Tactical |
You plan to shoot WAAAAAY out there at human-sized targets (that are, hopefully, not shooting back at you) and you might do it in some very adverse lighting and environmental conditions |
3-15×50, 5-25×56, 5-20×50 (10×42 if you are originalist or want to go light) |
Here are a few of additional guidelines
· atmospheric and lighting conditions that allow usage of magnifications above 15x or so are pretty rare where I live. Even in categories where I recommend high magnification variables, I mostly keep them below 15x. Higher magnifications are really useful for reading the conditions though even when you can’t easily use them for shooting.
· for long range applications you need scopes that have a large reticle adjustment range (70MOA/20mrad or more) and finger-adjustable exposed turrets.
· most of my recommendations above are somewhat generalized and within each application type there are further divisions. For example, some target shooting disciplines almost exclusively use ultra high (often fixed) magnification scopes.