Air Gun Glossary

Below is the Bicester Target guide to common terms and abbreviations used in air gun shooting.

A

Accuracy

General term, usually referring to the inherent ability of a rifle to consistently group all its shots close together on a target at a given distance under perfect conditions. It takes no account of human error, wind conditions, etc. Also applied to a given load, brand of pellets, etc., or to a combination of rifle and pellet. In shooting, the ability of the shooter and his rifle to deliver precision fire on a desired target. Accuracy can easily be measured as the ability to group all shots close to a desired impact point. The deviation from the desired impact point or the size of the group is a function of range. Accuracy is the product of uniformity.

Action

The combination of the receiver or frame and breech bolt together with the other parts of the mechanism of a rifle that normally performs loading, feeding, locking, firing, unlocking, extracting, and ejection.

Adjustable Objective

Fine focusing ring on the objective lens of a telescope that helps to eliminate parallax.

Adjusted Aiming Point

An aiming point that allows for gravity, wind, target movement, zero changes. 

Aggregate

The sum total of all targets in competitive shooting; final score.

Automatic Safety

A device on some rifles intended to return the safety to the "On" (safe) position when the action is opened, or finished firing.

 

B

Backlash

The distance the trigger travels after let-off.

Ballistic Coefficient

A mathematical factor representing the ratio of the sectional density of a pellet to its coefficient of form. Simply put, BC expresses a pellets length ( relative to diameter ) and aerodynamic shape, thus indicating its ability to overcome air resistance in flight. The higher its BC factor, the better a pellet retains its velocity and energy, and the flatter its trajectory.

Ballistics

The science that deals with the motion and flight characteristics of projectiles. It can be divided into three phases:

1) Internal ballistics

2) Exterior ballistics

3) Terminal ballistics.

The main aspects of ballistics that concern the rifleman are pellet velocity, stability, kinetic energy, trajectory and penetration/wounding effect.

Barrel

That part of a rifle through which a projectile or shot travels under the impetus of compressed air, or other like means. May be rifled or smooth-bore.

Barrel Band

Metal band that secures the barrel to the fore-end of a full-length rifle stock, or in the case of some PCP rifles to the main air cylinder.

Barrel Erosion / Barrel Wear

The gradual eroding away of the rifling lands immediately ahead of the chamber throat, resulting in accuracy loss.

 Barrel Time (Lock time?)

The interval between the time the pellet starts to leave its seat until it reaches the muzzle. This is significant in the case of a springer because is it linked to recoil time, which affects the point of impact.

Bead Sight

The small cylindrical top portion on some forms of front sights.

Bedding

Refers to the fit or fitting of the metal parts of the barrel and receiver with the wood stock.

Benchrest Rifle

A rifle designed for optimum accuracy while being shot from the shoulder and supported by a specifically designed table (rest). Shooting event utilizing rifles and ammunition designed to deliver extreme accuracy at long ranges.

 Bipod

A two-legged support attached to the fore-end of a rifle, used mainly for long range and/or accurate shooting.

Blue

The chemical oxidation to colour ferrous metal parts various shades of blue or black.

Bolt Action

A rifle in which the breech closure is: in line with the bore at all times; manually reciprocated to load, unload and cock; and is locked in place by breech bolt lugs engaging abutments usually in the receiver. There are two principle types of bolt actions, i.e., the turn bolt and the straight pull type.

Bore

The interior of a barrel forward of the chamber.

Bore Diameter

Internal diameter of a barrel measured from the tops of diametrically opposed lands, i.e. the smallest internal diameter. If the lands are not opposed, the diameter of a circle inscribed to touch the tops of the lands. It is the inside diameter of the barrel before the rifling is cut.

Bore Sighting

A method of aligning a barrel on a target by aiming through the bore. May be part of the sight alignment procedure. When sighting in a scope tools like a collimator can be used.

Breech

The chamber end of the barrel.

Bullseye

In target shooting, the aiming point or centre of the target.

Butt

(Pistols) Bottom part of the grip. (Rifles) Rear of shoulder end of stock, which rests against shooter’s shoulder.

C

Calibre

1. A term used to designate the specific pellet for which a rifle is chambered, also the approximate diameter of the circle formed by the tops of the lands of a rifled barrel. In terms of pellets it is a numerical term included in a pellet name to indicate a rough approximation of the pellet diameter. Proper style for calibre designations is no decimal point. eg: 177, 2, 20, 25.

 Carbine

A rifle of short length and light weight.

Chamber

The cavity at the breech end of the barrel bore that has been formed to accept and support a specific pellet.

Cheekpiece

A raised part of the side of the stock of a shoulder-arm against which the shooter rests his face. Usually associated with a Monte Carlo-type stock. Its purpose is to raise the shooter's eye to the height necessary to maintain the triangle of force.

Chronograph

Electronic instrument used for measuring the velocity of a pellet. An important part of a airgunners equipment as it helps to determine the power level of a rifle and keep it with the legal limts. It can also help with tuning an airgun to test for consistency of shots.

Collimator

Device used in roughly sighting in telescopic sight without firing a shot. It comes with a pin for every calibre it is to be used for. The pin is inserted in the barrel to keep the collimator aligned with the bore, and then the scope is set in such a way that the cross-hairs/reticle are aligned with that of the collimator.

Compensator

A device attached to the muzzle end of the barrel that utilizes propelling gases to reduce recoil.

Concealment

Protection from view. This is not necessarily the same as cover. Cover provides concealment, but concealment does not always provide cover.

Corrosion

The eating away of the bore by rust or chemical reaction.

Cross Dominance

A shooter with a dominant hand and a dominant eye that are not on the same side; for example, a right-handed shooter with a dominant left eye.

Crown

Configuration of exit part of the muzzle. The barrel is not merely cut off and left with the sharp edges, but the edge from the inside is rounded towards the outside. The form and angle of this has an influence on accuracy and stability of the pellet. The concentricity of the crown is very important, as variations will negatively influence the pellet as it exits the muzzle. The rifling at the end of the barrel can be slightly relieved, or recessed. The purpose is to protect the forward edge of the rifling from damage, which can ruin accuracy.

D

Deflection

The change in the path of the pellet due to wind or passing through a medium.

Drag

The aerodynamic resistance to a pellets flight.

Drift

Lateral movement of a pellet away from the line of bore, caused by its rotation on its own axis, and always in the direction of the rifling twist (compensated for by sight adjustment). Also used to describe the influence of wind on a pellets flight path.

Dry firing

Aiming and firing the rifle without a pellet in it. This is an excellent technique to improve marksmanship skills. Some rifles recommend not dry firing, so check with your rifles instructions before trying it.

E

Effective Wind

The average of all of the varying winds encountered.

Energy

Kinetic energy or force carried by a pellet at that point in its trajectory. In common use and popular shooting literature it is expressed in foot-pounds, one ft/lbs being the amount of force required to lift a one-pound weight one foot above the ground. Formula: Energy ( in ft/lbs ) equals pellet weight ( in grains ) multiplied by the velocity ( in feet per second ) squared, divided by 450240 (gravity). Often wrongly equated with killing power, energy is not a reliable gauge of this, as it does not take into account penetration or pellet performance.

Exterior Ballistics

The branch of applied mechanics which relates to the motion of a projectile from the muzzle of a rifle to the target, i.e. the performance of the projectile during flight.

Eye Relief

The distance that the eye is positioned behind the ocular lens of the telescopic sight. A two-to three-inch distance is average. The shooter adjusts the eye relief to ensure a full field of view. This distance is also necessary to prevent the telescope from striking the shooter face during recoil in some rifles.

F

FT - Field Target

A competition where outdoor, knock down targets are set in a series of lanes (see our guide to FT) Competitors use high powered scopes to range find targets between 8-55 yards. (see also HFT)

Feet Per Second (FPS)

Also referred to as ft/s and some written as FPS, it is a unit of measure for velocity.

Fixed Sights

Non-adjustable sights.

Flyer

A shot considerably outside a normal group on a target, not representative of the rifles or pellets potential accuracy.

Follow-through

The continued mental and physical application of marksmanship fundamentals after each shot has been fired. This is important in air rifles duw to the increased barrel time.

Related Words Barrel Time

Foot Pounds

(ft/lbs) Unit of measure for energy, being the amount of energy required to raise one pound in weight one foot above the ground against the normal pull of gravity. Used for pellet kinetic energy.

Fouling

Deposits of material or lead in the bore, chamber or works of a rifle after discharge. Excessive fouling influences accuracy.

Frame

The metal part of the rifle that contains the action.

Free-floating Barrel (FFB)

A barrel that is completely free of contact with the stock. This is critical to accuracy because of barrel harmonics. As the pellet is travelling down the barrel, the barrel is vibrating like a tuning fork. Any contact with the barrel will dampen or modify these vibrations with (usually) a negative impact on shot-group size or point of impact.

G

Grain

Measure of weight applied to pellet. 7,000 grains = 1 pound. 1 gram = 15.43 grains.

Groove

The low point of rifling within a barrel

Groove Diameter

The diametrical measurement of the bore of a rifled barrel, measured from the bottoms of opposing grooves (i.e. the largest internal dimension). If the grooves are not opposed, the diameter of a circle inscribed to touch the bottoms of the grooves is taken. This measurement should be fractually larger than the true diameter of the appropriate pellet.

Group

A cluster of pellet holes made by the same rifle/pellet combination, formed from numerous shots fired at a target using the same point of aim, for checking accuracy. A 5-shot group of 1 inch at your shooting range eg 45 yards (measured from the centres of the two widest spaced holes) is generally regarded as acceptable airgun hunting accuracy. It is a statistical fact that group size will increase with the number of shots fired.

Group Sizes

It is the maximum distance between the centres of the two farthest shots in a group. The easiest way to do this is to measure from the outside edge of one pellet hole to the inside edge of the farthest one away. Another method is to measure the distance from outside edge to outside edge of the farthest apart holes, then subtract the pellet hole diameter. ( Note that the pellet hole diameter is often smaller than pellet diameter - check it for yourself! ) This latter method allows recording groups smaller than the pellets diameter itself.

 

H

Hammer

A component part of the firing mechanism which strikes the firing-pin or transfer bar.

HFT - Hunter Field Target

A competition designed to replicate the challenges of shooting live game using knock down targets between 8-45 yards. This is a lower cost version of FT (Field Target) where guns and scope setups more closely match those used to shoot live game and vermin  (See our guide to HFT) See also FT.

Hide

The term used to describe a hunting position, normally concealed from the quarry.

Hold-off

A shooting technique used to compensate for pellet trajectory by using a modified point of aim above or below the desired point of impact. Also used to describe the modified point of aim used to compensate for wind or target movement. Also known as "Kentucky Windage."

Hold-over

When aiming at a target beyond the ‘zero’ or ‘sighted-in’ range of a particular rifle/pellet combination, holding over is the height one must aim above the target (without making mechanical adjustments to the sight) to drop the pellet onto the target.

Related Words Pellet Drop

Hold-under

The modified point of aim used below the target to compensate for a projectile on its upward axis of its trajectory. This is also used when shooting at angles (slopes).

Hooded Sight

A front sight that is equipped with a metal canopy. Designed to eliminate light reflections, as well as to protect the sight pillar.

Inherent Accuracy

The inherent ability of a specific calibre to be more accurate than other calibres in the same class. This is mostly relevant at bench-rest-level situations, where you're measuring fractions of an inch in group size differences. For hunting purposes, it's not really significant.

 

I

Internal Ballistics

The science/study of ballistics which deals with all the aspects of the phenomena occurring within the gun barrel, including pressure development and motion of the projectile along the bore of the rifle, i.e. all events until the moment the projectile exits the muzzle.

Iron Sights

A term that is broadly used to describe metallic sighting instruments, covering common open sights as well as aperture-type receiver sights (as opposed to scope sights).

J

Jack of all trades

A shop (on line or high street) that knows almost nothing about guns, actually shooting, or indeed anything else they sell.

The people who run it have never laid in the mud on a Sunday morning shooting an HFT or FT competition and will sell you whatever makes them the most profit.

K

Kentucky Windage

An estimate of the modified point of aim required to compensate for wind or for target movement. Synonymous with hold-off.

Keyhole

Elongated hole made in a target by a pellet that is tumbling in flight, hence strikes the target other than point first. Caused by inadequate rotational stabilization of the pellet (usually due to insufficient barrel twist; the twist is "too slow"), deflection of the pellet by objects in the pellets path, beyond the effective range for the rifle, or other factors.

Killing Power

Vague term applied to a pellet’s ability to kill quarry quickly with a single shot, assuming adequate pellet placement. Often wrongly equated with pellet energy. Killing power cannot be measured in precise terms, as neither it nor pellet energy take into account factors such as penetration, pellet performance, etc.

Kinetic Energy

Related Words Energy

L

Lands

In a rifled barrel, the raised spiral ribs left between the grooves in the bore. This is the part of the barrel that actually engraves the pellet, imparts the spin to the pellet, and ultimately stabilizes the pellet.

Lead

The modified point of aim in front of a moving target needed to ensure a hit. This depends on the range, and the speed of, the target. Generally this is considered bad practice for airgun hunting as quarry should staked and be still while taking the shot.

Leading

Traces of lead deposited in the bore by pellets, particularly if dirty or not adequately lubricated. A build-up of such deposits results in poor accuracy, but some leading is considered good practice as it creates a uniform condition inside the  barrel. (Related Words : Fouling)

Legal limit

In the UK an air pistol cannot exceed 6ft Lb and an air rifle must not exceed 12ft lb. Guns with higher power will require a firearms certificate. It is the owners responsibility to ensure that rifles and pistols do not exceed these values. Criminal  charges and substantial serious consequences await those found in the possession of FAC power guns. See our guide to air gun law.

Length Of Pull

The distance from the centre of the trigger to the centre of the buttplate or recoil pad.

Length Of Stock

The greatest dimension of the stock material.

Lever Action

Usually a repeating type of action with a reciprocating breechblock powered by a finger lever.

Line Of Bore

Imaginary straight line following the axis of the bore. Of theoretical value only, as a pellet begins to drop below the line of bore from the moment it exits the muzzle. Also known as ‘line of departure’.

Line Of Sight

Straight line from the shooter’s eye, along the sights to the point of aim.

Lock

A general term referring to the total firing mechanism.

Lock Time

The period of time between sear release (when the trigger is pulled) and the fall of the firing pin on valve (determined by lockwork design). No shooter can hold a rifle absolutely steady, and the longer the lock time, the more opportunity there is to disturb the aim during the firing pin’s travel, resulting in accuracy discrepancies.

Long Gun

A term used to describe rifles.

M

Magnus effect

A moving, rotating pellet in the air, drags some of the air around with it, in its direction of rotation. This increases the speed in that region, and thus the pressure is lower. Consequently, there is a net force on the pellet in the direction of spin, perpendicular to the forward movement of the pellet. This is called the Magnus effect.

Mid range trajectory

In its curved path, the highest vertical distance reached by a pellet above the line of sight. The term is a misnomer as the highest point in a pellet’s trajectory does not occur at "mid-range" but slightly beyond ( due to the bullet’s progressive slowing, the curve is in the form of a parabola, not a perfect arc ). MRT figures also apply to given loads and also depend on the height of the scope ( or sights ) above the bore. Useful for determining how low one needs to aim when a small target is closer than the zero range of the scope.

Mil

An angular unit of measurement equal to 1/6400 of a complete revolution (there are 6400 mils in 360 degrees). The mil is used to estimate distance and size based on the mil relation formula: 1 mil equals 1 meter at 1,000 meters. There are 3.375 MOA in 1 mil.

Minute of Angle (MOA)

Referred to also as MOA, it is a angular unit of measure used to describe the accuracy potential of rifles, and pellets. One MOA equals 1/60th of a degree ( 21 600 minutes in a circle ) and subtends 1.047 inches at 100 yards, or, for practical purposes, 1" at 100 yards. In hunting terms, a rifle/load which, at 100 yards, can consistently place five consecutive shots in a cluster measuring 1" between the centres of the two outermost holes ( "minute of angle groups" ) is considered extremely accurate. For Benchrest competitions the figure is obviously much less.

Muzzle

The end of a gun barrel from which the pellet emerges.

Muzzle brake

Device at the muzzle end usually integral with the barrel that uses the emerging gas behind a projectile to reduce recoil.

Related Words Compensator

Muzzle energy

Also referred to as ME, is kinetic energy or force carried by a pellet as it exits the muzzle of a rifle.

Related Words Energy

Muzzle Velocity

The speed of a projectile as it leaves the muzzle of the rifle.

N

Natural Point of Aim

The direction that the body/rifle combination is oriented while in a stable, relaxed firing position.

Natural Respiratory Pause

The temporary cessation of breathing after an exhalation and before an inhalation.

O

Objective Lens

The lens at the front of the telescope, facing the target. It is usually larger in diameter than the ocular lens.

Obturation

The sealing of propellant gases within the chamber of the rifle.

Ocular Lens

The lens at the rear of the telescope, nearest the shooters eye.

 Off-hand position / Off-hand shot

A shooting position in which the shooter stands upright and does not rest the rifle or his arms on or against any object.

Off-hand rifle

A target rifle designed to be held, not rested.

Open sight

Rear sight of traditional “leaf” type with open-topped V-notch or U-notch, as distinct from a scope or aperture ( peep ) sight.

P

Palm Rest

An adjustable support for a target rifle extending downward from the forearm.

Parallax

The apparent movement of the target in relation to the reticle when the shooter moves his eye in relation to the ocular lens. When the target's image is not focused on the same focal plane as the telescope's reticle, parallax is the result. Some rifle telescopes have a field parallax adjustment that makes parallax error an insignificant factor when proper eye relief and stock weld are used.

Pellet Drop

Term used to describe the measure of a pellets fall after it crosses the line of sight for the second time, i.e., beyond the zero or sighted-in range, due to the effect of gravity.

Pellet Drop Compensator

Any device that is integral to the rifle telescope that is designed to compensate for the pellets trajectory.

Plinking

The informal shooting at inanimate objects located at arbitrary or indefinite distances from the firing point.

Point Blank

A term especially related to hunting. The distance to which one can shoot at quarry, hitting in the target area, for example the vital ( heart/lung/head ) area, without any holdover. The mid-range trajectory and the pellet drop will both fall within the specified area.

Point Of Aim

The point on a target on which the sights are optically aligned when firing.

Point Of Impact

The point on which the pellet actually lands. By adjusting the sights, the point of impact can be made to coincide with the point of aim at a preselected distance; hence we say the rifle/sight/pellet combination is “zeroed” or “sighted in” at that range. Abbreviated to POI.

Projectile

A pellet in flight. Often wrongly used to mean a pellet per se. A pellet does not become a projectile until it is in flight.

Q

R

Range

The distance between the shooter and the target. Also short for shooting range.

Rangefinder

Device for determining range, or for optically measuring ( or estimating ) the direct distance to a target.

Ranging

The technique that a shooter uses to compensate for pellet trajectory by using adjustable/ranging telescope.

Rate Of Twist

In a barrel, the length over which the rifling grooves make one complete twist ( i.e. the length of the bore used to turn the pellet one full revolution ) e.g. 1:10 or one revolution in 10 inches. Differs from calibre to calibre. Pellet weight must be appropriate to the rate of twist or pellet will not stabilise in flight. The heavier the pellet, thus the longer, the faster the twist rate must be.

Recoil

The rearward thrust of a some rifles caused by the propulsion of a projectile in the opposite direction. Refer Newton’s 3rd Law of Physics: for every action there is an equal but opposite reaction. Commonly called “kick”. The amount of recoil felt by the shooter depends on factors such as the weight of the rifle ( which absorbs some of the recoil ), the design of the stock, the shooting position, etc. Incidentally complete analysis based on conservation of momentum would have to include the angular momentum the pellet acquires, which depends on the twist rate and length of the barrel.

Remaining Energy

A projectile's energy in foot pounds at a given range.

Reticle / Reticule

In telescopic sights, the element which is optically referred to the target. It may consist of straight or tapered cross-hairs (wires in the tube forming a central cross ), dots, or other marks used to determine the point-of-aim, size of, or range to the target. It is also markings in a microscope eyepiece used to establish location or scale. Commonly used to measure rifling.

Rifle Cant

Any leaning of the rifle to the left or right from a vertical position during firing. This should be eliminated because of the potential for increasing misses at longer ranges.

Rifling

Spiral grooves in the bore of a barrel to impart a rotary motion ( spin ) to the pellet to provide it with rotational stability. This will ensure that the pellet flies true with a point-first attitude.. Methods of manufacturing are Button rifling, Cut rifling and Hammer forging.

S

Scope

A shortened form of the word "telescope", meaning a telescopic sighting device for a rifle or, simply "riflescope". While a telescope magnifies an image, a riflescope is made with an integral fire-direction indicator called a reticle which, most often, appears as crossed-hairs or crossed-wires. A riflescope is securely mounted on a rifle and adjusted so that its vertical cross-wire is aligned with the path of the projectile. The horizontal cross wire is then set to coincide with the projectile's point of impact at a specific distance. It magnifies the target and places it and the reticle in the same optical place, facilitating very precise aiming.

Scope Mounts

Devices for securing a scope to a rifle, comprising scope rings and bases.

Sight Picture

The visual image observed by the shooter when the sights are properly aligned on the point-of-aim.

Sight-in

In rifle shooting, the process of getting the pellets point of impact to coincide with the rifle’s point of aim ( or line of sight ) at a pre selected distance, by means of sight adjustment. Applies to any given combination of rifle, pellet and sight system.

Stalking

The hunter's art of moving unseen into a firing position, engaging his quarry undetected.

Stock Weld

The contact of the cheek with the stock of the rifle.

T

Target

In HFT or FT this can depict an animal (normally rabbits, rats, crows etc) or a geometric shape. In competition targets the kill zone is a circular cut-out which when hit causes the face plate of the target to fall down. Kill zone apertures can vary from 15mm to 40mm depending on distance, discipline or distance.

A wide range of paper targets are used for 6Y (pistol), 10 M (pistol and rifle) , 25 Y and 50Y for competition  

Telescopic sight

A sight built into a telescope which incorporates some form of reticle, a focusing wheel and perhaps magnification controls. 

Trajectory

The track or path taken by the pellet in flight. It is described by the position of the pellet as being above (+) or below (-) the line of sight at any given distance. Air gun pellets (like all projectiles fired from a gun) create an arc as the pellet leaves the barrel, climbs and then falls under the influence of gravity. The shape of this arc is very different between .177 and .22 calibers. 

Trigger

The device normally operated by the shooter's index finger that initiates the firing of a gun.

Trigger weight

The force that is required to fire the gun, normally measured in grams. Some competition rules fix the minimum trigger weight (normally 500g) to avoid accidental firing.

Two stage trigger

A type of trigger which has (normally) about half the trigger weight to fire the gun taken up by a relatively long rearward movement and the remainder by a crisp sudden let off. This is a device to enable easier shooting, by giving the shooter some idea as to how much weight has been taken up before the shot is fired.

 

U

V

Velocity

The speed of a pellet, usually measured in feet per second.

W

Wad Cutter

A pellet design which features a sharp shoulder. Designed to cut a clean, round hole in a paper target.

 

Windage

The adjustment on the telescope or iron sights to compensate for horizontal deflection of the pellet.The distance or amount of horizontal correction that a shooter must use to hit his target due to the effects of wind or drift.

X

X (times)

The power of optical magnification (for example, 30x 50x, 10X, 3X-9X).

X-Ring

Center of a target. The bulls-eye.

Y

Yaw

The action of a projectile spinning erratically around its own axis.

Z

Zero

The range at which the point of aim and the point of impact are one and the same. Verb: To sight in a rifle/scope/pellet combination so that the pellet’s point of impact coincides with the point of aim at a pre-selected distance. Called this because at that distance, zero hold-over is required when aiming.


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