Selecting Your New Riflescope: The Basics
Adding optics to your firearm is one of the best investments you can make. Used properly, it adds to shooting safety for it allows you to better see what is to left, right, in front of, and being your target. With a single sighting plane, target acquisition is far faster. With appropriate magnification and the right reticle, your firearm becomes more accurate in use.
HOW MUCH MAGNIFICATION?
Often, we are under-scoped and over-magnified. If I asked most hunters if they could properly place a bullet on a whitetail deer at fifty yards with iron sights, they would say “of course” and perhaps even be a bit put-out by the question. Yet, even a 6x scope produces that same image for you . . . at 300 yards. More magnification doesn't mean a more appropriate scope for all applications, by any means.
Given the same objective size, increasing magnification gives you a smaller exit pupil in concert with the magnification increase, perhaps a darker image at the high end, and decreases your field of view. It is one thing shooting at stationary paper targets at a known distance in daylight on a clean range from a steady rest, but hunting is rarely that way. Animals move, stop, feed, change direction, and they don't care much about exact ranges. While your paper bulls eye might be an inch at the range, a whitetail deer's “bullseye” is its 8 – 10 inch kill zone.
For years, when fixed power scopes were the norm before variable power scopes were considered reliable, 4x was the standard big game hunting scope east of the Mississippi with 6X the standard for western, or more open hunting. The variable power 2-7 was extremely popular for years, with the 3-9 power remaining the standard right now more or less. As the 3-9 x 40 configuration is the most competitive, it also tends to be a good value due to its popularity and the economy of scale. The ideal scope power range for you is a function of animal kill zone size and range. For bear hunting over bait, or running game very little magnification is desirable, while for long range varmint hunting a variable power scope that hits 12x or 14x on the high end is of tangible benefit. If your hunting is in the timber, a 1.5 – 6x scope is ideal, with the 3-9 or 2-10 arena scopes versatile enough for the majority of moderate to longer range big game hunting applications.
WHAT IS THE MOST IMPORTANT FACTOR IN SCOPE SELECTION?
The best thing a scope can do is hold its zero. A scope with reticle float is generally worthless, the reticle needs to return to the same point of impact after the recoil pulse and resultant scope flex and stress after every shot. One thousandth of an inch at the muzzle of your rifle equates roughly to one inch at 100 yards, so a name brand scope with a good reputation is often the most savvy choice.
Most of the weight of a scope comes from glass, so the less mass the internals of a scope has, the easier it is to keep them under control. In terms of objective size, a 32mm or 40mm objective makes it easier to build a scope that can hold its zero, than the larger and heavier objectives. The adult human eye can dilate to 4 – 5 mm, so you need larger objectives to maintain that exit pupil diameter at higher magnifications. A 50mm scope, 10x magnification, yields a 5mm exit pupil. The cost and weight of heavier glass is often a good thing to avoid, unless you really need higher magnification for your applications.
The general quality of a scope is not just design and image, but also aesthetics, the evenness of the finish, etc. How positive the click adjustments are, the power ring and diopter adjustment that moves freely and smoothly without binding reflect on basic quality of machining and quality of assembly.
WHAT ABOUT COATINGS AND SCOPE BRIGHTNESS?
Scopes have been marketed in code of sorts. “Coated” means each lens surface has one coat of a reflection-reducing coating such as magnesium fluoride. Surface reflection can be reduced by applying coatings to the lens surface. You might think that coating the lens surface would block light, but in fact it increases light transmission. This is because light is reflected first by the coating surface, and then by the lens surface itself.
Multi-coated scopes mean some of the lenses have more than one coating to further reduce light losses due to reflection, while “fully multi-coated scopes” have multiple coatings (up to ten or so) to allow light transmission of up to the 99.9% per lens surface you've heard talked about. That is just per lens surface, so the best scopes have actual throughput of 90% or so. Fully multi-coated scopes are the standard in quality scopes today, the rest is often a debate among manufacturers as to who has the best coating technology. In general, you want fully multi-coated scopes if you are looking for a quality scope.
WHAT ABOUT EYE RELIEF?
For a low recoil application, such as a .22 rimfire rifle, getting knocked in the head by your scope isn't a strong likelihood. It is more comfortable to look through a scope than at it, so a small amount of eye relief can actually be considered an advantage. For lighter weight rifles with higher intensity cartridges, minimum eye relief of 3.5 inches or so can keep you from getting scope eye. In a tree or in the hunting fields, your stockweld may less than ideal as compared to target shooting, so generous eye relief can quite literally help you avoid a headache.
WHAT TUBE DIAMETER, ONE INCH OR 30MM?
Though the merits of larger tube diameter scopes are loudly touted, it doesn't mean much as far as the image quality of a scope. A larger, 30 mm tube is stronger tube, several times stronger than its one inch counterpart and it may have a bit more internal adjustment range. A larger tube also means larger, heavier scope rings to mount it to your rifle with. As a practical matter, it often gives you a stronger tube but not much else as far as practical field advantage.
Largely a matter of personal preference, reticle selection is important. In low light applications, a thin-wire reticle often disappears before the usable image does. While scope brightness gets a lot of attention, the brightest scope in the world is meaningless if you have no usable reticle. If low light shooting is a factor, you'll want to consider a reticle that is thick enough so you can still use it. One of the most demanding applications is black bear hunting deep in the woods. You'll often have a black blob in twilight, with a dingy dark background. Your job is to quickly put a black crosswire on the correct part of the black blob against the dark gray low-contrast timber. For something like this, your scope can't be too bright and your reticle can be too visible. You'll want a generously thick reticle or perhaps an illuminated reticle to make things a whole lot easier.
RANGE COMPENSATING RETICLES
With most of the “ballistic reticles,” the reticle is of a constant size, the second focal plane, so they only work when the scope is set to a certain power-- typically cranked all the way up. For “maximum point range” style of hunting as suggested by Jack O'Connor and others, your projectile never is more than three inches above or below the center of your cross-hairs. That's a “6 inch maximum point blank range” sight in, that you would use for an adult deer that has an 8 – 10 inch kill zone. It is fast, center of the body hold and just go pick him up, and what magnification your scope is set on matters not.
There are more advanced optics, those with First Focal Plane Reticles can be used at any power setting and there are integrated laser rangefinder scopes that get better all the time, but for many hunting applications and ranges the very complicated looking, holdover reticles can be needless complications when a rapid shot is indicated.
Size matters on two distinct levels. Aesthetically, the scope that matches the rifle makes for a pleasing package. To take a lightweight mountain rifle and slap on a massive, heavy, large objective monster not only looks silly, it gets well away from the overall lightweight package you bought the rifle for in the first place. The length of scope matters, for a short, stubby scope may not have enough mounting distance on your long action bolt action rifle without using base or ring extensions if you are using two-piece bases. If using a Picatinny rail, scope mounting distance becomes moot.
The greatest hunting accessory of the last 20 years is the laser rangefinder: no more guessing. You want to consider the battery life, ranging response time, waterproofing, the quality of the monocular, the reticle, and how well it fits your hand. Again, brands with good reputations are the safest bet, for name brands guard their reputations jealously and have earned it.