Airgun Sighting Systems

Last updated: 19th January 1997

Open sights (aka Iron sights)

Supplied on most airguns as standard, open sights consist of a "V" or "U" notched rearsight with a post or blade foresight. Normally the rearsight is only adjustable for windage (left-right adjust) and elevation (up-down adjust, aka distance adjust). On more advanced target airguns, the width of the rearsight notch can be varied, or the rearsight can be swapped for another notch, with a different sized/shaped notch. An

alternative to the notched rearsight, called a peep sight can sometimes be mounted on airguns (see below). The distance between foresight and rearsight is referred to as the "sight radius".

When your eye, rear sight, front sight and target are in proper alignment, you have a sight picture (i.e. You see the sights aligned on the target). Disturb any of those elements and you no longer have a sight picture.

Correct sight picture

Open sights can be sighted in for use with one of two ways of shooting:

1. "Target" sighting: used when fine precision in shot placement is required. Because the sights themselves (the front blade in particular) can block the shooter's view of part of the target, they are set so that the pellet will strike slightly above the front blade. This reduces the amount of target that is obscured by the sights.

Sight picture with target (target sights)

2. "Combat" sighting: used when hitting the target (and fast) is more important than hitting the target with great accuracy. Normally used with live-round firearms for combat use, the sights are set so that the centre of the top of the front blade is on top of the pellet's point of impact.

Sight picture with target (combat sights)

When sighting-in an airgun with open sights, the following rules apply:

If the pellets are hitting left of the bull: move the rearsight to the left.

If the pellets are hitting right of the bull: move the rearsight to the right.

If the pellets are hitting high of the bull: raise the rearsight.

If the pellets are hitting low of the bull: lower the rearsight.

(In case you're wondering, think about it; it does make sense!)

Peep sights

Peep sights (aka diopter sights, aka aperture sights) can sometimes replace the rear notch on an airgun using open sights, and are normally only found on precision, match grade airrifles as they offer increased accuracy. They basically consist of a "disc" with a small opening in its centre that is adjustable for windage, elevation and sometimes the diameter of the hole (aperture).

Red-dot sights

Red-dot sights work by effectively placing a red dot onto the target, either by shining a beam of light onto it, or by projecting a beam of light back into the shooter's eye. Because of this, most reddots powered by one or more watch batteries, although some, such as the Webley Speedpoint, rely on collecting and focusing ambient light.

Features:

No magnification of the target, making them only really suitable for close range use.

Well suited to quick target acquisition (especially laser pointers, in which case the gun can be aimedand fired at the target, without having to be held up to the shooter's eye). Good for snap-shooting, but are really not best suited for slow, deliberate aiming and long-range precision, in which case a scope is the best option.

Normally have built-in mounts.

Sometimes described by the size of the dot used:

a 1 minute dot covers a 0.25~' area at 25 yards
a 5 minute dot covers a 1.25" area at 25 yards
a 10 minute dot covers a 2.5" area at 25 yards etc...

Reflex sights

Reflex sights project a beam of light into the shooter's line of vision, and are often designed to be used with both eyes open. While one eye looks at the target, the other sees the dot, and the two images become superimposed on each other. Alternatively, if the sight can be viewed "through" (i.e. it has a clear back), then it can be used in the same way as a conventional scope, with just one eye open.

Reflex sights are normally fairly cheap, with prices starting from around £15.

Laser pointers

Features:

Work by simply projecting a thin beam of light onto the target to show where the pellet will impact.

Can be used in conjunction with a scope; if the laser is slung underneath the gun's barrel, the scope on top of the guns receiver, and both are sighted in for x metres If the dot appears on the target below the centre of the scope's cross hairs, the target is closer than x metres, if it's above, then it's farther away.

Not recommended for hunting; it's difficult to holdover when you can't see the dot because it falls in open air above the target. Laser pointers are a lot more expensive than reflex sights, and can easily cost over ten times as much.

Apart from the high cost to buy them, the only other disadvantage laser pointers have is that the dot can be difficult to see if it is projected onto a brightly lit target.

The Bushnell HOLOsight

Advertised as using the same technology used in F-14 Tomcat fighter aircraft, the Bushnell HOLOsight is the newest form of sighting system for airguns. It works by ~llurninating a hologram of the reticule pattern (recorded on the HUD window) with laser light, making the holographic image appear visible, downrange on top of the target.

The sight can be fitted with any of the following reticules:

Bushnell HOLOsight Reticules

Standard

2D Ring with dots and tick marks. Ring measures (ermmmmwell it's either supposed to be 34 or 65
MOA, depending which of the Bushnell advertising you read!) Dot measures 1 MOA.

Dual Rings

2D Design with two rings (20 MOA and 65 MOA).

Open Crosshairs

2D All purpose design that does not cover up the target area. Inner circle is 30 MOA.

Rising Tracer Dot

3D Reticule that gives the illusion of a line coming out of the gun and ends in a 1 MOA dot that is
underneath half a standard reticule.

Features:

Latest sighting system available.

Uses a laser illuminated hologram as a reticule.

Fast target acquisition.

Interchangeable reticules require no re-sighting.

No light cast on target.

Cannot suffer from parallax error.

No magnification of the target, making it only really suitable for close range use.

Good for snap-shooting, but are really not best suited for slow, deliberate aiming and long-range precision, in which case a scope is the best option.

Comes equipped with wide mounts for live-round firearms; a mounting adapter is required to mount it onto an airgun.

EXPENSIVE!!! About 500 UK pounds for the sight and standard reticule, with extra reticules costing 100 each!

Airgun Sighting Systems: Telescopic Sights (aka Scopes)

Last updated: 8th January 1997

Contents:

General information
Sighting in (aka zeroing)
Scope terminology

General information

The majority of airrifle owners (about 80%) fit scopes to their rifles. This is primarily because they allow the shooter to realise the full potential of the gun's accuracy. (In some cases though, the shooter may have no choice; many major gun makers don't fit open sights to their guns.) Another major advantage of fitting a scope is that, since there is no need to continuously shift the eye's focus between the foresight, rearsight and target, aiming a scoped gun is easier than using open sights. Prices range from £15 pounds for a cheap, budget scope, to over £1200(!) for a night vision scope.

Fitting a scope does not mean that you can't use open sights. It is possible to buy special raised mounts that have a hollowed out space underneath the scope, so that the open sights can still be clearly seen while the scope is mounted. This is particularly useful if the gun is to be used for both long and short range work; the scope can be sighted in for long range use, and the open sights for short range.

While it is possible to buy these mounts, it is fairly common to just use standard mounts and remove the front (open) sight (especially if it is covered by a hood). This is in order to prevent it from showing up through the scope as an out-of-focus blur, obscuring part of the image.

NOTE: Before we go any further, please remember: scopes do not double up as carrying handles! Fit a sling or get a proper case to carry your airgun in! Using an airgun's scope to lug it around by is a sure-fire way of knocking it's aim well off centre, necessitating sighting in again.

If you wish to fit a scope to an airgun, you must use a proper airgun scope and not one designed for use with live-round firearms. This is for two reasons:

1. The "double-recoil" of a spring piston airgun can easily break the reticule of a live-round firearm's scope. Many such scopes only brace the reticule to allow for the gun to recoil in one direction; backwards.

2. Scopes made for live-round firearms are often intended for hitting targets 100m or more away, and designed so that parallax is not a problem at these ranges. This means that serious parallax problems can occur at 20m or less, especially if the scope's magnification is greater than 4x.

Scope specifications are given in the form: "mxd" where m gives the magnification (power) of the scope and d gives the diameter of the objective lens in mm.

The higher a scope's magnification is:

The smaller the scope's field of view at any given distance.
The nearer you will appear to be to the target (e.g. a 4x scope will appear to bring the target 4 times closer you).
The higher the potential to place pellets on target with greater accuracy.
The more difficult it will appear to be to keep the gun on target. It is not easy to hold a gun perfectly steady; your breathing, and even your pulse, makes the gun wave around. The more powerful the scope is; the more this "wobble" will be amplified.
The dimmer the image will be.

Some scopes have variable magnification, in which case m will be of the form: "x-y", with x and y being the minimum and maximum magnification that the scope can achieve.

The larger the diameter of the objective lens, the better, as the more light the scope will be able to transmit to your eye, and the brighter the image appears. This also means that a larger objective will allow you to use your airgun in low-light situations where there is little ambient light falling on the target.

In addition to its normal specification, a scope can further be described by one or more of the following acronyms:

BDC = Bullet Drop Compensator.
TV = a wide, TV shaped rectangular view seen when you look through the scope.
PA = Parallax Adjustment.
RF = Range Finder.
WA = Wide Angle view.

The following scope specifications are suggested for various uses:

General use
        4x15, 4x20, 4x28, 4x32
Hunting
        4x40, 6x40, 2-7x32, 3-9x40, 4-12x
        4x magnification should suffice, with a minimum 32mm objective lens. For low light
hunting, a 45+
        objective should be used, and an illuminated reticule would be a great bonus.
Long range use, or field target
        4- 16x, 6-24x, 18-40x
        A minimum objective of about 40mm is needed, preferably with parallax adjustment and a
distance
        calibrated focus on the objective bell.

When fitting a scope, the following points should be noted:

The image seen through the scope should be clear (an even circle around the lens surrounded by another even circle which is the closest edge of the eyepiece should be seen).
Make sure that the scope mounts allow easy access to the breech for loading pellets, etc.
Check that all screws on the mounts are tight. They should not be over-tightened, and only give a moderate hold. On a recoiling gun, the mounts will have to be clamped on more than would be necessary on a recoilless one, in order to minimise scope creep. If the dovetail grooves on the gun are made of plastic, it is possible to damage them if the mounts are excessively tightened.
MAKE SURE THAT THE TOP TURRET IS VERTICALLY ALIGNED WITH RESPECT TO THE GUN! See the description of canting below.

One final point: Never attempt to disassemble your scope! They are typically waterproof and often contain nitrogen gas to help this. Dismantling will release this gas. If your scope does come apart do not put anything down tube; this will inevitably break the reticule. If any repairs ever need doing to your scope; send it back to the manufacturer - don't try to fix it yourself.
Back to top ,

Sighting in (aka zeroing)

You should always check your gun's zero:

At the start of every shooting session; slight knocks and bangs that can occur easily when the gun is being handled or moved from place to place can easily knock the sights off zero. Also, if the gun uses CO2, any change in the ambient temperature can affect the gun's zero.
After adding or removing a silencer.
After changing your shooting position; even your grip on the gun can change the pellets' point of impact.
When changing to a different pellet brand/make.

To sight in, the following procedure is suggested:

1. Set up your backstop with a large target a short way away from your shooting position. A target about the size of an A3 sheet of paper, no more than about 1 5m away should be aufficient. Try to use a proper zeroing target (consisting of a series of horizontal and vertical ruled lines), checked with a plumb-line. (A piece of string with a weight attached will serve to check it's vertical) to make sure it's vertical. Note: You should change targets as often as is needed so that you can always see where each individual pellet is hitting.

2. Check the screws on the scope's mounts are properly tightened.

3. Set the scope to its lowest magnification. If the scope has an adjustable focus ring on its ocular bell, set this the minimum, and then adjust to obtain the clearest image.

4. Get into a stable position with a tin of pellets within easy reach.

5. To start the actual sighting in, load the gun (checking the pellet loaded is not distorted in any way) and check that your range is clear.

6. Put the centre of the scope's cross-hairs on the centre of the target (or line them up where a pair of horizontal and vertical lines intersect if a zeroing target is being used). Avoid canting the gun.

7. Let off the shot.

8. Repeat steps 5-7 at least four more times.

9. Check the target and if necessary, remove the scope's protective turret caps and adjust the scope's windage and elevation settings as appropriate, using the average of the group for reference.

For scopes with " 1 Click = 1/4" @ 100 yrds":

o 1 Click = 1/4" @ 100 yards

o 1 Click = 1/8" @ 50 yards

o 1 Click = 1/16" @ 25 yards, etc...

Often an airgun can shoot low, but there is no "up" adjustment left. This often occurs on rifles with a "droped" barrel, and can easily be overcome by placing a small piece of photographic film between the scope and one of it's mounts. The same trick can be applied if, for some reason, the gun shoots too high, but there is no more "down" adjustment left.

10. Repeat steps 5-9 until the pellets are consistently hitting dead centre.

11. Next, move the target back to the distance you intend to do most of your normal shooting from. For hunters and target shooters this may be around 30m or so, for plinking; around 20m. Repeat steps 5-11.

12. Replace the scope's protective turret caps. When you have finished this, the scope is fully sighted in, and ready for use.

Note: Sighting in should be done in still air; don't sight-in on a windy day! Pellets can easily be blowed off-course. Sighting in should preferably be done indoors (provided you can find somewhere with aufficient space; a long, empty hall would be ideal).

Scope terminology

1/4 minute clicks
        This describes the sensitivity of the scope's turret adjustment; one "click" of the scopes turret shifts
        the pellets point of impact by 1/4" at 100 yards (= 1/4 MOA). Since the effective range of an airrifle is
        usually sub-45m, this sensitivity needs to be scaled down to be useful, but shows that the scope has
        the following property:
o 1 Click = precisely 1/4" @ 100 yards
o 1 Click = precisely 1/8" @ 50 yards
o 1 Click = precisely 1/16" @ 25 yards, etc

30/30
        See reticule.
arrester system
        An arrester system stops scope creep. It is simply a small block mounted immediately behind the
        scope's rear mount (and possibly pinned to the gun's receiver), in order to prevent it, and the scope,
        from moving backwards. Some scope mounts themselves have pins underneath which locate into
        holes in the gun's receiver to have the same effect.

bullet drop compensator

Externally adjustable windage and elevation turrets, making it easy to "dial in" a new zero at different distances.

cantina

"Canting" increases inaccuracy when shooting over longer distances, and is probably the main cause of missing targets at long distances.The scope is canted if it is not mounted with the vertical cross-hair perfectly upright with respect to the gun's receiver. In this case, the barrel will be out of alignment with the centre of the crosshairs.The gun can be canted if it is held badly, and not upright. To prevent the gun being canted, you can buy a special "scope leveller" (small spirit level) which fixes to the side of the scope. When aiming, you simply keep both eyes open and the leveller is superimposed on the scope's sight picture, allowing you to aim and keep an eye on the gun's alignment at the same time.

Diagram showing the effects of canting

dovetail grooves

Needed on an airgun if a scope is to be mounted onto it; what the mounts clamp onto.

duplex

See reticule.

exit pupil

A scope's exit pupil is the small cone of light seen in the eyepiece.To compute the diameter of any particular scope's exit pupil, divide the size of the objective lens by the magnification the scope provides. For example; a 4x20 scope has an exit pupil of 20/4 = 5mm. Obviously the exit pupil gets bigger the lower the magnification and larger the objective lens.

The smaller a scope's exit pupil is, the harder it is to acquire the image. Conversely, an oversized exit pupil makes target acquisition faster and easier. Although, having said that, the eye can't utilise any more light than what is obtained by an exit pupil of about 7mm, even at night.

eye relief

The amount of space left between the ocular lens and the shooters' eye. When looking through an airrifle scope, you should have around 2-3 inches' eye relief, that is; you should leave around 2-3 inches' between the back of the scope and your eye. This is especially important with spring piston airguns, where the recoil could cause the scope to hit you in the face otherwise.

mounts

These are what fix a scope to a gun's receiver. Mounts consist either of one or two pieces. One piece mounts are better for spring piston airguns as they can offer a better grip on the gun, and so reduce scope creep. One piece mounts are normally used with heavy scopes.

A lot of budget-priced scopes come complete with integral mounts.

When buying mounts, you should aim to get the best one that you can afford.

objective bell

The wider part at the front of the scope, housing the objective lens.

objective lens

The scope's larger, front lens. Basically, the larger this lens is, the better. This is especially true when the targets you shoot at are poorly illuminated, or the scope has high magnification.

Ocular bell
The wider part at the rear of the scope, housing the ocular lens.

ocular lens

The scope's smaller, rearmost lens, which focuses the combined image of target and reticule into the shooters' eye.

parallax

Parallax is the apparent shift of the scope's reticule on the target when the scope is kept perfectly still, and the image viewed through the scope is observed from different points. This effect is most noticeable at very short ranges, and can lead to great inaccuracy at long ranges.

Parallax is caused by the image of the target not being focused exactly on the same plane as the reticule.

Because:

1. A fixed focus scope can only be focussed at one distance, and

2. Because the distance between the object lens and the reticule is fixed;

If you point the scope at a target nearer or farther away than the focus distance, the targets image will not be focused exactly on the reticule. This will force you to focus your eye between the two planes; effectively reducing the scope's accuracy.

Parallax error cannot occur if your eye is aligned exactly with the target and reticule.

parallax ring
        Some scopes allow parallax error to be "dialled out" by adjusting the objective lens. This is done by
        means of changing a parallax setting (adjustable objective focus), on the objective bell. The adjustable
        bell is normally calibrated in metres/yards; helpful if you know the distance you are shooting from.

On high powered scopes, this ring can also be used as a secondary focus facility for estimating the range to the target.

reticule

A scope's reticule is the two thin cross-hairs inside the scope that are superimposed onto the target to show exactly where the pellet will impact.The reticule is usually mounted just in front of the ocular bell. It consists of either two extremely fine wires (which are virtually invisible to the naked eye), or an etched reticule which is made up of a glass disc with the reticule marked on it. Because a scope's reticule can be snapped extremely easily, nothing should ever be poked down the scope's tube.

The simplest scope reticule consists of two crossing lines, but another common type is the duplex reticule, where the cross-hairs are thinner in the centre than they are towards the sides of the scope. A 30/30 reticule is a particular type of duplex reticule; the thin-lined part of the cross-hair representing an area of 30" on the target when viewed at 4x magnification at a range of 100 yards. Scaled down for airrifle ranges, this is an area of approximately 1 3cm at 40m, or 8cm at 25m. This is useful when trying to estimate range, and the amount of holdover to give a target.

Another type of reticule is the graduated reticule, made up of a series of horizontal lines which form a ladder to provide aiming points at varying ranges.

Diagram showing several different types cf reticule

scope creep

        Scope creep is found on recoiling airguns due to the whiplash effect of the airgun's recoil. When the
        gun's trigger is squeezed, the trigger/sear mechanism releases a piston that flies forwards at high
        speed, causing the gun to recoil backwards. Then the piston is stopped suddenly by the air compressed
        by it, and rebounds backwards, making the gun snap forwards in mid-recoil. Over time, this causes
        the scope to slowly "creep" backwards towards the rear of the gun, putting the scope off zero and
        making re-sighting necessary.

tunets

The raised section about half way down the scope's tube. Used to adjust the reticule to coincide with the pellets point of impact.

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This article was originally published at Airguns, Airguns, Airguns web site
http://www.trailerpark.con,/phase 1 /airguns/sights.html
For some reason this site has disappeared, and I have not been able to locate it anywhere on the net. I don't know who and where the author is, but I think this is too good an article to disappear. Therefore, I decided to scanned the hardcopy I happened to file and put it here. I appologize to its author for doing it without his or her consent.