Scope terms and how to choose a scope
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How to decode the scope model numbers
Scope sights are extremely popular among airgunners because good scopes wring the last bit of accuracy from a gun. They also forgive a lot of common sighting errors, as seeing the sight and target clearly at the same time is a great aid to accurate shooting. This article will explain a lot of the confusing terms used to describe scopes, plus we will look at how some of these things really work. No one scope is perfect for every job, so by understanding the terminology you can better understand which scope will best help you accomplish what you need. We will look at the common terms first, then we'll explore the types of scopes to use for different shooting situations.

In the model name "4 X 32," the number four refers to the magnification power of the scope. A 4-power scope enlarges the image four times. An 8-power scope enlarges things eight times, making it seem to be closer than when seen through a 4-power scope. That sounds good, but there are drawbacks to power. The higher the magnification, the less area you can see through the scope. If your scope is too powerful, you may be able to see ants crawling on a blade of grass, but you'll never know which blade it is because they all look the same. Higher magnification also eats light. An 8-power scope will show the same image darker than a 4-power, if everything else is the same. There are ways to increase the amount of light that passes through the scope, such as larger lens diameters and even a large scope tube diameter, but if that goes too far you get a large scope that is more difficult to mount. Every lens in a scope robs a tiny bit of light that tries to pass through, so the higher the magnification, or the more lens coatings, usually the darker the image.

Choose four to six power for hunting and general shooting. Nine to twelve power is good for long distance shooting and 20 power is great for paper targets that aren't going to move. The number 32 in the 4 X 32 model name refers to the diameter in millimeters of the objective lens. That's the end opposite the end you look through. The larger the objective lens, the more light that can pass through it and the brighter the image at a given magnification. As power increases, the need for light also increases; otherwise you'll be looking at a large dark shadow. That's why high-powered scopes have large objective lenses. A 4 X 32 is brighter than a 12 X 40, because the 32 mm objective lens does more for the lower-powered scope than the 40 mm lens does for the higher-powered one. Large objective lenses present a mounting problem. The scope rings must be higher to permit the scope to clear the rifle. Rifles like the Air Arms TX 200 are very straight and need very high scope mounts for clearance. Other rifles like those from AirForce have special raised scope bases that provide a lot of their own scope clearance. They can easily accept larger objective lenses.

Many scopes have variable power, which is indicated in their title. Instead of a 4 X 32 scope, you might see a 4 - 12 X 32 scope. In that case, the scope's magnification is variable from four to twelve power and the objective lens is 32 mm. Take a look at some of the scopes on this site and see how easy it is to know their performance characteristics, just from these numbers in the model name. This ring on the back of a variable power scope determines what setting is selected. Variable power scopes are very popular because they give you the benefit of several power options. For sighting in your gun, a low power is desirable initially, because you start shooting very close. When you want to reach out with precision, higher magnification is usually wanted. With a good variable scope, you get the best of both worlds.

The reticle is commonly referred to as the crosshairs. It usually consists of one vertical and one horizontal line. In the distant past, these were actual threads of silk or spider webs, but today they are more often either thin metal wires or even lines etched on glass. They are housed in a tube called the erector tube and the adjustment knobs move this tube in the desired direction. That's why the reticle lines appear centered on nearly all scopes. A few scopes from Europe have reticles that actually move in your field of view when they are adjusted, but most shooters prefer reticles that are always centered. A plain reticle is just two lines that intersect in the center of view. There are many types of reticles but only a few are popular. The plain reticle is just what it sounds like, two intersecting lines with no other features. The only choice you can make with this type is how thick or thin the line are. Since this reticle is often used for paper targets, thin lines might be best. If you intend to do general shooting with it, however, get a reticle thick enough that you can find it when looking into dark foliage. A duplex reticle has thick lines that taper to thin lines near the center of view. It is the most popular reticle because it addresses the most needs. The duplex reticle is probably the most popular type today. In a duplex the reticle lines are thicker on the edges, then taper to thin in the center of the image. The thick sections are easier to see against a dark background and the thin lines provide a more precise aiming point. In really dark situations, you may not be able to see the thinner lines at all, but the thick outer lines point to the center where they intersect. The mil dot reticle is becoming more popular with airgunners every day. It gives additional aim points, plus it can be used to determine range, if the shooter knows the math. The mil dot reticle is a military design that is now becoming popular among airgunners. Along the lines of a plain reticle, small dots are placed at precise distances from one another. They enable the shooter to measure angle downrange while looking through the scope. The mil unit of angular measurement is used because a mil is smaller than a degree of angle. There are 6,400 mils in a full circle. The literature that comes with the scope will tell you how many mils are between each dot (see article on Mil dot scope) To determine range with a mil dot reticle requires the use of an algebraic formula that most shooters either don't know or don't care to do, but the dot reticle is still quite valuable. As the shooter becomes familiar with the reticle over time, he will develop a sense of how to best use the dots. Most shooters use the dots on the horizontal line as alternate aim points for windy situations.

When you focus a scope, you aren't making the target appear sharper like you might think. Focusing means adjusting the eyepiece to get the reticle lines as sharp as possible. You normally only focus a scope one time and leave it that way unless something happens to change the focus. The focus ring on this Leapers target scope tells the shooter which way he is adjusting the eyepiece. To focus a scope, look through the scope at a light-colored wall. You are looking to see that the reticle is in sharp focus. If it isn't, adjust the focus ring until it sharpens as much as possible. A hint here is to not stare through the scope for longer than a few seconds, or your brain will refocus your eyes to sharpen the image. Some scopes have a diopter indicator on the focus ring. Once the scope is focused, it shouldn't need changing unless the shooter's eyes change, so a prudent shooter remembers where the ring is set (if there are markings). That allows the shooter to refocus the scope by adjusting the ring back to the mark rather than going through the whole focusing process again.

Don't confuse parallax adjustment with focusing the scope. When parallax is adjusted, it cancels as much parallax as possible between the reticle and the target to give you the best possible chance of hitting the target. Now - what the heck is parallax? Parallax is the term that describes the difference in angles between objects that are seen up close and those seen far away. When you look at telephone poles pass by on the side of the road, those closest to your car seem to pass very fast, while the ones far away seem to go very slow. That difference is due to parallax. The large optional sidewheel on this Leapers scope makes parallax adjustment easy! The reticle in your scope is like a telephone pole that's very close. If you move your head on the stock while watching the target through the scope, it's probably possible to see the reticle move against the target. That affects where you perceive the aim point to be, and that affects your accuracy. Parallax correction reduces this phenomenon to the greatest extent possible. To use a parallax ring, which many scope manufacturers call an AO (for adjustable objective) ring, turn the ring until the target appears sharp in the scope. The true distance to the target may not always agree with the numbers etched on the parallax ring of the scope, but the scope is adjusted when the image is at its sharpest. Some newer scopes now have the parallax ring on the turret with the windage and elevation knobs. It works the same way; the only difference is the location.

Choosing a scope is not easy for anyone. There always seems to be another model that has some features you also want, but can't get on the model you select. That's because a scope is full of compromises. If you can afford one, buy a variable-power scope every time. On low power it will be bright and on high power it is easier to see a well-lit target. Hunters need less power than target shooters. Live targets move and a wide field of view is important if you want to see them through a scope. Low-powered scopes have the widest field of view. A 4-12 power scope is just about ideal. If you have a powerful spring air rifle, get a scope that can take the two-way recoil. And get a scope mount that has a positive recoil stop to prevent slippage. No clamping mount will hold up to sustained recoil. Make certain the scope you choose can be mounted to your airgun with the scope mounts you intend using. Spring guns are often touchy about scope clearance. If you aren't sure which reticle to select, remember that it's hard to go wrong with a duplex. The rest of scope selection will come as you gain experience with what is available. Since no one scope can do everything, the best choice is the features you know you need. In this article we name the parts of scope mounting systems, present standards, and mount a scope, following simple step-by step instructions. Many shooters scope their air rifles. In fact, a scope sight is the number one accessory an airgunner purchases. But people often feel that mounting that scope on their rifle is a technical challenge beyond their capabilities, when, in fact, it is one of the easiest things there is. Much of the confusion comes from firearms. You can't shoot a firearm indoors at any great distance, so for decades gunsmiths have been mounting and aligning scopes using an optical device called a collimator, which helps align the intersection of the bore axis and the sight axis at some planned range. Scales on the collimator allow gunsmiths to adjust the scope so the rifle has a high probability of being somewhere on a paper target at the selected range, which is often 100 yards for centerfire rifles and 25 to 50 yards for rimfires. Remember - the best the collimator can do is get you on paper at those distances - you have to finish the job by adjusting the scope while shooting the gun. With an air rifle, you can sight-in starting at 10 feet and finish at 10 yards, if you want to. I'll show you how in another article. There is no need for a collimator because you are so close to the target that, even if the scope needs a huge amount of adjustment, you will still be hitting the target paper.

Before we start mounting, let's clear up some confusion about the naming of scope mounts. What are mounts, rings and bases; and how do they differ? The term "mounts" includes both scope bases and rings. On firearms the distinction may be important, but since most adult airguns are designed to mount scopes, the bases are already installed. On less expensive Crosman, Benjamin/Sheridan and Daisy guns, a separate mount base is often required. It is attached to the gun first, then the scope rings attach to it. But for most adult air rifles, the base is already on the gun when you buy it. On this TX 200 spring rifle from Air Arms, there are two parallel dovetail grooves with three scope stop holes between them. Select one of these three holes for the scope stop pin on the rear mount (or if you use a one-piece mount, put the pin at the rear) to engage. The standard scope base for airguns is a set of two parallel 11mm dovetail grooves. If the gun is a recoiling spring gun, there should also be some kind of scope stop to interface with the rings. This "standard" is very loose, which is why there are so many proprietary scope rings manufactured for specific brands and even certain models. When you buy scope rings, have the salesperson check to make sure that what you are buying is intended for your airgun. One final word on Weaver and Picatinny bases. These are firearms bases that perform the same function as an airgun scope stop. They keep the scope rings from moving on the base during recoil. Shooters coming from the firearms side of the house are very familiar with these bases, but no airgun is manufactured with them today. B-Square does make an 11mm to Weaver adapter base that allows the use of Weaver-base rings. Rings are what hold the scope in place. For airguns, scope rings come with their own bases that are designed to attach to the scope base found on the rifle (or attached as an option in the case of guns like the less expensive guns mentioned above).

II have selected non-adjustable rings for this article. They are easier to explain than adjustables. We may do a special article on B-Square AA adjustable rings in the future, but this time we'll look at non-adjustable mounts, which are by far the most popular and commonly used. I selected two-piece rings, because they are more flexible to use. One-piece rings are installed the same way, but they allow fewer mounting options because wherever the one ring goes, the other is always attached. I have selected the most difficult type of rifle to scope, a recoiling spring-piston air rifle, to demonstrate all the details of scope mounting. Precharged and other pneumatics plus CO2 guns are easier, as are recoilless spring rifles. I will use a TX 200, which is not a hard spring rifle to scope, but I will cover the details the same as if we were scoping a real kicker. One thing should always be in your mind. Will my scope have enough clearance when mounted on the rifle with the rings I select? Look at the photo of the scope mounted to the TX 200 to see what I mean. If the objective lens were much larger, this scope would require higher rings to fit this rifle.

Step 1. Attach the scope ring(s) to the rifle. The TX 200 has three vertical stop pin holes, as seen in the photo. Put the stop pin of the rear scope ring in the one that seems best for your situation. For guns that don't have holes, the pin may rest against the mount base that's permanently attached to the rifle. The pin's purpose is to stop rearward movement of the scope rings and therefore, of the scope itself. Airguns that don't recoil (like precharged guns) don't need a scope stop. If you are mounting to one of these, you need to remove the stop pin from the base of the ring. Remove the top caps of the ring(s) as shown in the photo before installing them on the rifle. The reason for this will be made clear in the next step. Snug the rings so they don't move, but don't tighten them all the way yet. >
Step 2. Position the scope. Lay the scope on the open rings and position the eyepiece by sliding the scope back and forth. You may have to move one or both rings to get this right. Position the rings so the scope's eyepiece will be the correct distance from your shooting eye when the gun is held naturally. This is usually between two and three inches from the eyepiece lens, but it is the spot at which the image in the scope appears as full and bright as it gets. To see what this looks like, move your head back and forth along the stock, as you look through the scope with both eyes open. Then, position your head on the cheekpiece where you want it to be and move the scope back and forth until the image appears bright and full. Now, put the top caps back on each ring without moving the scope forward or backward. Tighten them until the scope is held secure but can still be rotated with your hand. That isn't very tight!

StStep 3. Align the scope's vertical reticle. Align the vertical reticle with both eyes open and the gun held naturally to your shoulder. Rotate the scope until the vertical reticle seems to bisect the gun perfectly. Now you can tighten the base of the rings securely to the gun. Once the position of the scope is determined, the rings are tightened to the gun and the top caps are installed. Center the vertical reticle before tightening the caps.

Step 4. Tighten the top caps to hold the scope. This is a step where care should be taken. There is no need to over-tighten the ring caps to hold the scope in place, but most people overdo this part. Tighten each screw partially, then move to the next one and go around the pattern of screws many times, rather than tightening each screw all the way on the first try. You will put even tension on the caps and be less likely to dent the scope tube this way. If there are two screws on the side of the ring, tighten only one, then tighten the one on the opposite corner of the other side of the cap (see graphic below). Leave the other two screws for the moment and tighten two screws on the other ring next. Then come back to mount one and tighten the two screws you left loose. Then back to the other ring and keep rotating until the scope is secure. It takes less tightening that most people think, so err on the side of too loose, rather than too tight. Keep going around the pattern, tightening very little each time. I hold on to the small end of the Allen wrench to keep from over-tightening. Some folks try to get the same amount of space between the caps on either side of the mounts, but I don't worry about it very much. Once the screws are tight the job is finished. Now the scope can be sighted-in. Now that you know how to mount your scope (see All about scopes, Part 2.) let's learn out to sight it in. Firearms are usually sight-in at 50 or 100 yards. They require the use of a device known as a collimator to align the scope with the bore, but that's not necessary when sighting-in an air rifle. We will start sighting at just TEN FEET, so there is no chance of missing the target paper. You MUST WEAR safety glasses, because you are going to shoot into a pellet trap at a range of just 10 feet. You will be hit by pellet fragments at this distance, so don't take any chances. WEAR SAFETY GLASSES AT ALL TIMES The steps of sighting in are keyed to the photos. This whole procedure takes less than 10 minutes to complete.

Step 1. Draw one or two small dots on a piece of cardboard large enough to show where your pellets are going. I draw two dots about 2.5 inches apart and stacked vertically. The target in the photo measures about 6 inches wide by 9 inches high, though it was cut roughly from a box. There is no precision to this step. You just want enough room on the target so no shots are lost. At 10 feet, they can't go too far. Hang this target in a safe bullet trap. If your scope has parallax adjustment, adjust it as close as it will go. If it has variable power, adjust it as low as it will go. The aim point will still be a little fuzzy at this distance, but do the best you can. Always aim at the top dot. Expect your first shot to be as much below the dot as the center of your scope is above your bore. If that's three inches, that's also how low the shot should go.

Step 2 After seeing where the first two shots went, I applied some right correction to the scope's horizontal adjustment knob and some upward correction to the elevation knob. At 10 feet it takes a LOT of clicks to move the next shot just a little way!

Step 3 Move the target out to 10 meters (or yards, it doesn't really matter). I shot two more shots and found I'd adjusted the scope too far to the right. This was corrected by adjusting the horizontal knob to the left. It doesn't take as many clicks to move the shot at this distance.

Step 4 One more shot shows I am realigned with the aim point vertically. Once the target is moved farther away, the shots will rise, but should stay pretty much in line from side to side. I like to have my shots land about 1.5 inches low at 10 meters, but this one is lower than that.

Step 5 Move the target to a range of 20 to 30 yards away. I moved it to 25 yards. As you can see, my group is very close to the aim point at this distance. That is a 5-shot group, and I am satisfied with it. If I were sighting in this rifle to use, I would make some final small scope adjustments to bring the strike of the shots over to the aim point. If the shots are on the aim point at 20 to 30 yards, the rifle is sighted-in. It will shoot low from the muzzle out to about 20 yards. From there to 30 yards the pellet will move up or down so little that it will seem to strike in the same place, for all but the most critical shooting. This method works best for airguns shooting in the 800 to 900 f.p.s. range. At 900 f.p.s., the pellet will still be very close to the aim point out to 35 yards. Beyond 30 or 35 yards, the pellet will land below the aim point again. Remember to wear those safety glasses at all times during this sight-in procedure. In fact, it's a good thing to do every time you shoot any kind of gun - pellet or firearm. It is especially important when shooting at the initial 10-foot distance, because the lead fragments will come back at high speed.