Below is a list of terms that are commonly used in relation to firearms and ammunition.

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A –

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Accurizing – The process of increasing the inherent accuracy of a firearm.

Annealing – The use of heat to soften parts of a brass case, typically done to the case neck. This is to counteract the more brittle nature of a case head after it has been reformed multiple times. However this must be done carefully to prevent softening of the case head

Antimony – A metallic element, added to lead, to increase its hardness

Anvil – A part of a primer  that strikes against the priming material to create friction and the initial spark needed to ignite the powder

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Ball – A type of Full Metal Jacket round used by the military; Used by Olin Industries to describe their spherical powder

Ballistics – The study of projectiles in motion

Ballistics, Interior – The action of a projectile as it is inside of the firearm, from chamber to barrel

Ballistics, Exterior – The forces on a bullet as it files from the muzzle to its target

Ballistic, Terminal – The Actions of a bullet as it interacts with its target

Ballistic Coefficient – The ratio of a bullet’s density relative to its coefficient of form; describes the bullet’s ability to overcome wind resistance in flight

Barrel Cylinder Gap – The space between the cylinder and the forcing cone of a revolver

Bearing Surface – The sides of a bullet that come into contact with the rifling of a firearm

Bedding – The place where a rifle’s action and or barrel comes into contact with the stock; the act of fitting a stock to a rifle

Belted Case – A brass case with a reinforced belt just forward of the extractor groove, normally found on magnum cartridges

Berdan Primer – More common on European brass cases, a berdan primer requires a small protrusion in the primer pocket to serve as the anvil (see Anvil)

Boat Tail – A taper at the heel of a bullet and common on military and match grade bullets

Body – The section of a brass case between the head and where the shoulder begins to taper

Bolt – The part of a gun’s action that houses the firing pin assembly, extractor, and locking system

Bore – The interior of the barrel; used to describe the inner diameter of the barrel before the rifling is cut, also called “bore diameter”

Bore Sight – Sighting a firearm in by sighting through the barrel

Boxer Primer – A type of primer common in American brass cases, both military and civilian, does not require a protrusion in the primer pocket like a berdan primer

Brass – A common shorthand for the brass case of a cartridge that houses the bullet, powder, and primer

Bullet –  The projectile that is shot out of a firearm, usually made from lead and copper

Bullet Path – The trajectory of a bullet from muzzle to target, usually an arc at longer distances

Bullet Puller – A tool to remove a bullet from its brass

Burning rate – A term used to describe the rate at which a powder burns, usually subjective, such as slow or fast burning power

C –

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Caliber – The rough diameter of the groove or bore of a barrel, expressed in millimeters or decimals of an inch. This number is often rounded to a more even number, such as .30-30, .308 Win, and .300 Win Mag all use the same diameter bullet. This is often adapted to distinguish the cartridge from other cartridges that use the same diameter bullet, such as .30-06 and .357 Sig and does not necessarily denote the exact diameter that a cartridge uses

Cannelure – A small groove around the side of a bullet that is used for crimping, lubricating, and identification

Cap – An early version of a primer used for black powder firearms, also called a percussion cap

Cartridge – A round of ammo that is complete, with the brass case holding a bullet, powder, and primer

Case – See Brass

Case Mouth – The opening in the brass to accept a bullet

Case Trimmer – A tool used to decrease the length of the brass

Case Volume – The volume of the space in a cartridge that can hold powder, this is determined by the amount of water that can be held in the case with a bullet seated to the maximum SAAMI cartridge length

Centerfire – A type of cartridge that houses a primer in the center of the head of the brass

Chamber – The section of a firearm’s barrel that houses the cartridge and prevents it from expanding too much when fired

Chamber Cast – A casting of a firearm’s chamber, used to take measurements of the chamber

Chamfer – Trimming or beveling a small taper on the case mouth to remove burrs

Charge – The amount of powder used in a cartridge

Chronograph – An instrument used to measure the speed of a bullet as it travels to the target

Components – Term used to denote all the materials used to construct a cartridge (brass, powder, bullet, primer)

Compressed Charge – An amount of powder that is large enough for the bullet to compress it when it is seated in the brass case

Core – The center, usually lead, of a bullet

Corrosive Primer – Older type of primer that will cause corrosion of the barrel due to the fouling being left in the barrel after firing a round using corrosive primers

Crimp – Turning the mouth of a case inward to grasp the bullet, usually into a cannelure

Cylindrical Powder – Smokeless powder that has a tubular shape to the pellets, manufactured by an extrusion process

D –

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Deburr – The removal of rough edges on a case mouth after it has been trimmed to length

Deburring Tool – A tool used to deburr the mouth case

Decap (Deprime) – To remove a primer from a brass case

Die – A tool used to reform a fired brass case and seat a bullet into the case mouth; In bullet making used to form a bullet

Double Base Powder – Smokeless powder using nitrocellulose and nitroglycerine

Drift – A term in ballistic to describe the lateral movement of a projectile in flight

Drop – The effect of gravity on a bullet

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Elevation – The adjustment needed to bring the point of aim into line with the point of impact

Energy – When used in ballistics this denotes the amount of foot pounds of force that a bullet has when impacting a target

Engraving – The marks on a bullet left by the rifling in a barrel after it has been fired

Erosion – The slow wearing away of the rifling due to the gases and friction caused by firing rounds through the barrel

Expander Ball (Button) – A portion of a decapping stem that is larger to expand the case mouth the required diameter to firmly grasp the bullet

Extruded Primer – A ring or crater on the primer where the primer has been forced back into the recess of the firing pin. This is an indication of excessive pressure on the primer

F –

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FPS – Feet per second; measurement of a projectile’s velocity

Fire-Forming – The firing of a cartridge to expand it to the full dimensions of the chamber

Firing Pin (Striker) – A small pin located in the bolt face that strikes the primer, in striker fired systems this is pin is held back under spring tension until released by the trigger and sear

Flake Powder – A type of smokeless powder that is formed in flakes or small discs

Flash Hole – The small opening in the webbing of the case to allow the spark from the primer into the body where the powder is

Fluted Chamber – A barrel with cuts made into the chamber to aid in extraction and reduce the amount of friction created during the chambering and extraction process.

Foot Pound – A unity of energy used to denote the amount of force that a bullet strikes a target with; equal to the amount of energy to raise a pound one foot in the air

Freebore – See Thorat

Full Metal Jacket (FMJ) – A type of bullet with a lead core encase in a jacket, usually copper

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Gas – The vapor formed by the burning of powder and expands in the chamber and barrel to force the bullet down the barrel

Gas Port – A hole drilled into the barrel to bleed off gases to operate the action of a semi-automatic or fully automatic rifle

Gilding Metal – A copper and zinc alloy used in bullet jacketing material

Grain – A unit of measurement for weight used in bullet weight and powder weight; One pound is equal to 7,000 grains

Grooves – The cuts in the barrel to create the rifling; the wider diameter of the two parts of the rifling

H –

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Hangfire – A delayed ignition of the powder after the primer has been struck

Headspace – The gap between the bold face and the case head; the distance between the bolt face and the part of the chamber that acts as the cartridge stop

Holdover – The amount over a target the shooter has to aim when the rifle is zeroed for a shorter range

Hollow Point – A bullet that has a hole drilled into the top to allow for greater expansion when impacting a target, common on defensive handgun rounds

Hydrostatic Shock – The shock wave created by the impact of a bullet on a mostly liquid target

I –

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Ignition – The first combustion  of the powder in a cartridge caused by the primer

Impact Extrusion – A way of shaping the copper jacket around the lead core of a bullet

Improved Cartridge – A cartridge that has been fire formed to better fit a specially chambered rifle. This normally results in less body taper or a sharper angle to the shoulder

Ingalls Tables – Ballistics tables computed by Col. James M. Ingalls and servers as one of the standard ballistics tables in small arms

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Jacket – The covering of a bullet, normally copper over a lead core

K –

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Keyhole – A “keyhole” shape to the impact on the target indicating that the bullet was not stabilized in flight

L –

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Lands – The raised portion of the rifling of a barrel

Leade – See Throat

Line of Departure – A straight line leaving the muzzle to infinity

Line of Sight – A straight line from the sights or scope to infinity

Load Density – The weight of the powder charge divided by the case volume

Locking Lugs – A part of the bolt that prevent the bolt from moving to the rear during the initial firing process

Lock Time – The time between the release of the firing pin and when it strikes the primer

M –

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Magnum – A firearm or cartridge case that provides greater power than other cartridges using similar diameter bullets, such as .44 Special and .44 Magnum

Max ORD – Maximum Ordinate or Mid-Range Trajectory being the point where the bullet reaches its highest distance above the line of sight. Typically half way down range

Meplat – The diameter of the blunt section of a bullet tip

Mercuric Primer – A primer using mercuric compounds; see Corrosive Primer

Metal Fouling – Metal, normally copper, deposits in the rifling of the barrel

Micrometer – A type of caliper used to measure thickness

Minute of Angle (MOA) – A unit of angular measurement that is equal to 160th of a degree, normally rounded to 1″ at 100 yards (1.047″ at 100 yards)

Misfire – A failure of the cartridge to fire after the primer is struck

Mushroom – The ideal shape of a hollow point after impact

Muzzle – The end of the barrel of a firearm

Muzzle Blast – The gas expelled just after the bullet leaves the barrel

Muzzle Energy – The energy that a projectile has when it first leaves the muzzle

Muzzle Velocity – The velocity that a projectile has when it first leaves the muzzle

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Neck – The portion of the brass case where it narrows, forward of the shoulder that grips the bullet

Neck Reaming – The removal of metal from inside the case mouth to create a uniform case wall thickness

Neck Sizing – The resizing of just the neck of the brass

Neck Turning – The removal of metal from outside the neck to achieve uniform case wall thickness

Non-Corrosive Primer – A primer that does not use corrosive compounds that will create rust if left on the firearm for extended periods. Most ammo after 1950 use non-corrosive primers

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O.A.L. – The overall length of the cartridge

Ogive – The curved nose of the bullet

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“+P” or “+P+” – Commonly misinterpreted as “Plus Powder”, however this is generally incorrect. Indicates an “over pressure” round that exceeds SAAMI or CIP specifications by roughly 10% for +P and 30% to 40% for +P+. Some +P or +P+ rounds may use more powder but the name indicates more pressure and more velocity. There is no SAAMI specification for +P+, however there is for +P. +P rounds have less pressure than Proof Rounds. Frequent shooting of +P or +P+ rounds will reduce the service life of the firearm. Finally they should only be used in firearms rated for +P by the manufacture.

Pierced Primer – A primer that has been punctured by the firing pin when struck

Point of Aim – The point where the trajectory of the bullet intersects with the line of sight

Powder – The combustible substance used to generate gas when ignited to propel the bullet down range

Powder Measure – A measuring device used to pour a set amount of powder into a single brass case

Powder Scale – A scale for weighing an amount of powder, normally in grains

Pressure – The force exerted by the gases and burning powder, expressed as “peak pressure” and measured in pounds per square inch

Primer – A small metal cup containing a priming compound which, when crushed, creates the initial spark to ignite the powder in the cartridge

Primer Indent – A depression in the primer after it has been hit by the firing pin

Primer Pocket – The recess in the case head that holds the primer

Projectile – A bullet in motion

Proof Load – A load used to test the strength of the barrel and the breech, roughly 20% more pressure over standard loadings depending on the cartridge; see also +P or +P+

Protruding Primer – Also called a popped primer, is a primer that has partially backed out of the primer pocket

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Ram – The section of a reloading press that is used to raise or lower a die during resizing and bullet seating

Ream – To remove material from the brass using a rotary cutting tool

Rebated Case – A case that has a rim of a smaller diameter than the case body

Remaining Velocity – The velocity of a projectile at a given distance from the muzzle

Remaining Energy – The energy of a projectile at a given distance from the muzzle

Resizing Die – A die used to reform a fired case to the proper dimensions

Rifling – The spiral grooved cuts in the inside of the barrel that cause the bullet to spin as it travels down the barrel

Rim – The flange that is behind the extractor groove on a cartridge. This is used to extract a case from the chamber after firing

Rimfire – A type of cartridge that has primer compound in the rim instead of a primer in the center of the case head

Rimmed case – A brass case with a rim that is a larger diameter than the case body

Rimless case – A brass case with a rim that is the same diameter as the case body

Round – See Cartridge (A round in the chamber”), or sometimes see Bullet (“Sending rounds down range”)

Round Nose – A bullet with a blunt, spherical tip

Rupture – A split in the case wall or neck

S –

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Small Caliber, High Velocity (SCHV) – A smaller caliber round, typically less than .30 caliber, that is fired at high velocity. Early experimentation with such rounds date back to the 1890’s, however modern SCHV rounds were not put into military use until the 1950’s with the introduction of the 5.56x45mm NATO

Seating Depth – The depth to which a bullet is seated into the case mouth

Seating Die – A die that can be adjusted to change the seating depth of a bullet

Sectional Density – The ratio of a bullet’s weight, in pounds, to the square of the bullet’s diameter, in inches

Semi-Rimmed Case – A brass case with a rim just slightly larger than the diameter of the case body

Shank – The straight section of a bullet behind the ogive

Shellholder – A device used in reloading to hold the case upright and guides the case into the die cavity. A specific cartridge requires a shellholder of a certain size

Shoulder – The part of the brass case that slopes down from the body to the neck

Single Base Powder – Smokeless Powder that contains nitrocellulose

Sight Radius – The distance between the front and rear sight, generally longer offers better accuracy potential

Spherical Powder – Smokeless powder pellets that are in the shape of a ball

Spent Primer – A primer that has used up its priming compound

Spin – The spinning of the projectile caused by the rifling of the barrel

Stabilize – The prevention of yawing or tumbling through the rotation of the bullet caused by the rifling

Swaging – Forming material under pressure

T –

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Throat – The portion of the barrel that is not rifled just ahead of the chamber

Time of Flight – The time that the bullet spends in the air from muzzle to the target

Twist – The rate of spiral of the rifling of the barrel, this is given as the length of the barrel required to complete one rotation

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Velocity – The speed of a projectile while it is in flight

Vernier Caliper –  A finely graduated measuring instrument used by handloaders

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Web – The portion of a brass case between the bottom of the primer pocket and the case interior. The Web also has a flash hole for igniting the powder by the primer

Wildcat Cartridges – Any caliber that is not mass-produced. These are usually created by enthusiast shooters that are looking to optimize an aspect of a pre-existing cartridge.

Windage – Horizontal adjustments to bring point of aim into line with the point of impact

Wind Deflection – Horizontal drift during a bullet’s flight caused by wind

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Yaw – The tendency of a bullet to tumble or spin end over end as it passes through a target. This is desirable when a bullet is passing through a target but not as it is flying to the target. Modern bullet design, especially in military applications, has favored this idea since the 1950’s and includes examples such as the 5.56x45mm NATO and the 5.45x39mm.

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Zero – The point where the line of sight come into line with the bullet trajectory at a specific distance