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.
WHAT DOES 4 X 32 MEAN?
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.
WHEN TO CHOOSE HIGH AND LOW POWER
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.
VARIABLE POWER
 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.
RETICLES
 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.
FOCUS YOUR SCOPE
 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.
PARALLAX ADJUSTMENT
 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.
HOW TO CHOOSE A SCOPE
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.
NNAMING THE PARTS
 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).
LET'S MOUNT UP
 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.
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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
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