Action – The mechanism that physically acts on cartridges (loads, locks, fires, and extracts). Varies by type of firearm, and a firearm tends to be categorized by this (e.g. Single Action, Double Action, Bolt Action, Lever-Action)
Assault Rifle – A select fire intermediate rifle-caliber weapon which uses a detachable magazine, commonly the standard service rifle in most modern militaries.
Automatic (Fully Automatic) – A mode of automatic fire wherein the firearms discharges rounds continuously at the firearm’s Rate of Fire as long as the trigger is pressed and there is ammunition available to be autoloaded into the chamber.
Ball / Ball Ammunition – See FMJ.
Battery / Battery Position – The position of the parts and cartridge in a firearm action at which the firearm is ready to fire. In most cases this means a cartridge in the firing chamber held securely in place by the breech block.
Blowback (blowback operated) – A variety of operation for autoloading firearms in which mechanical action is achieved directly by the force generated in firing a cartridge.
Bluing – An electrochemical conversion coating of metal surfaces that results in a dark blue/black finish resulting from an oxidizing reaction with iron forming magnetite. A very old method of corrosion resistance. A classic look.
Bolt – The part of a firearm that blocks the rear of the chamber while a cartridge is fired and propellent is expended, then moves out of the way to allow another cartridge to be placed into the chamber.
Bolt Action – A type of firearm action where the weapon’s bolt is manually operated to open and close the breech by handle.
Bore – The interior of a barrel of a firearm.
Break-Action – A type of firearm action where the barrels are hinged and able to be manually opened allowing manual or assisted extraction and manual loading of cartridges into the chamber.
Breech / Breechblock – The rear of an action which holds a cartridge in the chamber and absorbs the recoil when the cartridge is fired.
Breechface – The surface that makes contact wih the rear of a chambered cartridge in a firearm.
Breech pressure – The amount of rearward force applied when a projectile is fired.
Bullpup – A firearm layout where the action and magazine are located behind the trigger.
Caliber – The internal diameter of a firearm’s barrel or external diameter cartridge’s bullet, commonly stated in hundredths or thousandths of an inch (.45, .357) or millimeters (9mm, 20mm).
Carbine – A shortened variant of a rifle, in older examples, sometimes chambered in a less powerful cartridge.
Cartridge – A complete package consisting of a bullet (projectile), propellent (gunpowder), and primer packaged into a casing. Also referred to as a round, or coloquially as simply a bullet or shell.
Centerfire – A class of cartridges in which the primer is in the center of the rear of the cartridge case. This is in contrast to Rimfire cartridges in that the primer is a separate (replaceable) component. Most modern cartridges, with the exception of very small, low-powered (e.g. .22lr) rounds are Centerfire.
Chamber – The section of a barrel where a cartridge is inserted to be ready to be fired. Revolver chambers are often referred to as firing cylinders, or just cylinders.
Chambering – Placing a cartridge into the chamber of a firearm, in order to ready it for firing. Maybe done done manually by hand with an open action or by cycling the action of the firearm (if applicable).
Charging Handle – A part of a firearm whose operation results in the hammer/striker being moved into ready position (or ‘cocked’). Often manipulates the Bolt as well.
Choke – A constriction of varying types at the muzzle end of a shotgun’s bore in order to alter the spread of shot.
Clip – A device, usually a crimped strip of metal, used to store several rounds of ammunition together, with the purpose of quickly recharging a magazine (detatachable or internal), allowing for faster reloading than going one at a time.
Compensator – See Muzzle Brake.
Direct Impingement – A method of gas-operation for a firearm where gas is directed from a fired cartridge (usually via a tap a short distance down the barrel) directly to the slide or bolt carrier (as opposed to acting on a piston rod) in order to cycle the firearm’s action. Most commonly found in M16/AR-15 type rifles, and notably used in the Desert Eagle, one of the few gas-operated handguns.
Double Action (DA) – A mode of operation of a firearm’s trigger in which a the pull of a trigger both cocks and releases the hammer in one movement.
Double Action Only (DAO) – A mode of operation of an automatic handgun’s trigger in which the hammer is never allowed to be left in a cocked position. Every trigger pull cocks and releases the hammer, and the hammer isn’t left cocked by the firearm’s action, similar in function to how a Double Action Revolver works. Most commonly used by police agencies for safety reasons, and for ease of training in transitioning from Double Action revolvers. Primary advantage is uniform trigger pull regardless of first shot or follow up shots. Primary disadvantage is in the long, heavy trigger pull.
Double Action / Single Action (DA/SA) – A mode of operation of a firearm’s trigger which combines features of DA and SA in automatic handguns. When hammer is already cocked, Trigger acts as Single Action (SA), generally with a lighter, shorter trigger pull. After each shot and cycle of the action, the hammer is left cocked and the trigger will be an SA pull. However, if the hammer is let down (manually, or by use of a de-cocking lever, generally for safety reasons), the trigger will act as a Double Action (DA) trigger.
Drum Magazine – A high capacity firearm magazine in the shape of a flat cylinder, or “drum.”
Dry Fire – The act of activating the firing mechanism of a firearm without a cartridge loaded; dropping the hammer or striker on an empty chamber. In many cases this is seen as mildly harmful to the firearm, and is discouraged. This is especially true in rimfire weapons. Some manufacturers have outright debunked this, however, such as S&W outright claiming dry firing their Centerfire Revolvers does no harm, and Glock, as you’re required to dry fire as part of typical field strip procedure (though their manual notes to avoid excessive dry fire practice).
Ejector – The part in a firearm which, once pulled from the firing chamber by the extractor, causes the brass to be ejected from the firearm’s ejection port, usually by means of a spring, or simply by knocking the case, still held by the ejector, against a fixed pin/tab, using the rearward motion to flick the case free in the proper direction.
Ejection Port – The opening in the firearm, commonly in the upper receiver / slide, through which fired cases are ejected through after firing.
Ejection Rod – The mechanism by which fired or unfired cartridges are removed from the cylinder/chambers of a revolver, acting as both an extractor and ejector. Most commonly being a rod which is depressed when the cylinder is open that lifts all cartridges in chambers together.
Extractor – The mechanism within a firearm which removes the spent casing from the firing chamber after the cartridge has been fired, usually by means of a claw hooking the case rim. Normally works in conjunction with an ejector to eject the spent case from the ejection port and clear the path of the action for the next round to be loaded.
Eye Relief – The distance from an optic’s eyepiece to the user’s eye at which the scope picture is visible. This is important depending on the configuration, as scopes with long eye relief are required when used in “scout” configuration rifles or with pistols.
FMJ – Full Metal Jacket, a type of bullet consisting of a soft metal (most commonly lead) core encased in a thin shell of a harder metal such as copper alloy, the advantage being decreased lead fouling, especially in high-velocity loads, increased penetration, and increased uniformity of performance, as well as less risk of damage when steel/penetrating cores are used. FMJ, also called “ball” ammunition, is the most common military ammunition used since the Hague Convention’s banning of expansion/flattening ammunition (soft lead).
Forcing Cone – The conical section at the rear of a revolver barrel which directs the bullet’s entry into the bore. Necessary due to slight timing variances, potential distance from the cartridge to the bore based on the cartridge/bullet used, and the necessity of a minute gap between the cylinder and barrel in a revolver, as a revolver’s battery position is different than other firearms.
Forward Assist – A mechanism, commonly found as a button on an M16/AR-15 type rifle, located near the travel path of the bolt on the exterior of the firearm. When pressed, it interfaces with the bolt/bolt carrier to move it forward if able, in order to ensure the bolt is locked forward and the firearm is in-battery.
Fouling – A buildup of gunshot residue on the surfaces and moving parts of a firearm. Fouling material most commonly consists of propellent residue, bullet material traces such as copper/lead, and lubricant contaminated by these other sources of fouling.
Frangible – A type of bullet designed to break apart into tiny fragments on impact in order to minimize penetration and, potentially, increase energy delivery to the target. Most commonly used for safety reasons, as they reduce overpenetration risk and nearly eliminate ricochet potential.
Furniture – Vernacular for the parts attached to the firearm making up the stock / forend handguard of a firearm, likely in reference to these parts historically being made of wood, like furniture.
Gas-operation (Gas-operated) – A variety of operation for autoloading firearms wherein expanding gases from the the firing of a cartridge is used to provide energy to operate the firearm’s action. Usually by means of a tap at a particular distance down the barrel which either acts directly on the bolt/bolt carrier (Direct Impingement) or acts pneumatically on a piston which drives the bolt/bolt carrier (piston operated). In select-fire / automatic gas operated firearms, distance from the breech to the tap is a factor in the firearm’s rate of fire, with shorter distances equating to higher potential rates of fire, unless otherwise mechanically limited.
Gauge (Ga) – A unit of measurement of interior barrel dimension, similar to caliber. Specifically, in modern use, used as the unit of measure for shotgun bores, with 12 gauge being the most common. This unit of measure is derived using the following, nearly archaic, method of measurement- Gauge number is determined by how many lead spheres the size of the bore in question add up to an imperial pound. Hence, twelve 12-gauge lead balls equal 1lb, or a single 12-gauge ball equals 1/12lbs. This is why gauge number is inverse to diameter, why a 20ga is smaller than a 12ga (as it would be referring to a lead ball weighting 1/20lbs. vs. 1/12lbs.)
Grain (Gr) – Another very old method of measurement still in common use- this unit of measurement being commonly used to refer to bullet weight as well as propellent / powder measurement in a cartridge, abbreviated as “gr”. Traditionally based on the weight of a grain of wheat or barley, ~65mg. Defined precisely in 1958 as 64.79891mg. Scales used for cartridge measurement will display measurement in grains.
Grip – Area of the firearm that is meant to be held by hand, most commonly used to refer to the Pistol Grip, or the vertical area held by the trigger-using hand. Can also refer to a vertical foregrip or the forend handguard / furniture / stock of the firearm.
Grip Safety – A safety mechanism most commonly found as a lever on the rear of pistol grip, unlocking the firing mechanism of the firearm when pressure is applied, done so by having the firearm being handled in proper shooting position.
Half-cock – A position where the firearm’s hammer is partially cocked, but not to the point that it can be activated by a trigger pull. Many older firearms had a stop at this position to allow a half-cock for both loading (of revolvers without an opening cylinder, as this would allow the cylinder to be rotated so cartridges could be inserted to the chambers by a opening door), or safety reasons (to allow a firearm to be loaded with a cartridge and in-battery, without the hammer resting on a live cartridge.
Hammer – The part used by many types of firearms to strike the firing pin, subsequently setting off the cartridge. Named for resemblance and functional similarity to the handtool.
Hammer Bite – The injury caused to the shooter’s hand by a firearm’s external hammer scraping, pinching, or jabbing the web of the shooter’s hand between thumb and index finger. Older 1911 style (GI-style) and Browning Hi-Power pistols without beavertail/duckbill style grip safties are most known for this.
Headstamp – The markings on the bottom of a cartridge case, most commonly indicating manufaturer and caliber, sometimes (most commonly if military) the year of manufacture.
Hollow-point – A type of bullet made to expand upon contact with a target through use of a hollow cavity at the tip, the purpose being to decrease penetration in ensure energy delivery and increased wound-cavity size in tissue, causing additional trauma.
Intermediate Cartridge – A cartridge with a higher energy level and longer effective range than pistol cartridges, but less energy than battle rifle cartridges (such as the .308/7.62×51 and 7.62x54r). Shares more characteristics with rifle cartridges than pistol cartridges. Most common examples are the 7.62x39mm and 5.56x45mm NATO.
Iron Sights – A sight system using aligned markers to allow aiming of the firearm. “Iron Sights” may be metal or polymer (but most commonly the same metal as the receiver, hence the name) either fixed to the firearm or removable, and may be fixed position or adjustable. “Iron Sights” or backup-sights, are in contrast to optical or holographic sights, which are usually optionally affixed to the firearm in addition to, or in replacement of, the “iron sights.”
Jacket – A metal, harder than the core of a bullet, which surrounds a softer metal core. Most commonly copper wrapped around lead. Used in bullet types such as FMJ, TMJ, and JHP.
JHP – Jacketed Hollow Point, a type of bullet which is jacketed similar to an FMJ, but with a hollow recession at the tip to allow for expansion. Deperession may be also jacketed, or may be exposed lead of the core.
Length-of-pull – The length of distance between the butt of the stock and the trigger on a long gun. Important for ergonomics of a firearm. Collapsible stocks and firearms with adjustable buttpads allow customization of length-of-pull.
Lever-action – A variety of operation for a non-autoloading firearm whose action is operated by use of a lever located near the trigger, generally in two movements, the first extracting, opening the action, re-cocking the hammer/striker, and ejecting the spent case, the second/reverse closing the action and moving a cartridge from the magazine to the chamber.
Light Machine Gun – A type of machine gun that can be carried and operated by an individual. Contrast this with Heavy Machine Guns or Crew-served Weapons.
Lug – Any of the various design features of a firearm or firearm part that protrudes from the part for the purpose of attachment- for example a bayonet lug used for the attachment of a bayonet near the muzzle of end of a rifle barrel, or the lower barrel lug on a 1911 barrel that protrudes and allows for the slide catch to pass through, securing the 1911 together in the final step or reassembly from a field strip.
Machine Gun – A fully automatic firearm. Umbrella term, as Machine Guns take many forms, from Crew-served Heavy Machine Guns and Autocannons to Handheld Submachineguns and Machine Pistols.
Machine Pistol – A fully automatic, or burst-fire capable (Select Fire) firearm based off of a Handgun design. That is, tends to only have one grip, which also houses the magazine.
Magazine – The ammunition storage and feeding mechanism within a firearm. May be detachable (seperate from the firearm, sometimes incorrectly referred to as a Clip in vernacular), or fixed (integrated into the design of the firearm, loaded by hand with or without the assistance of a clip, for instance the tubular magazine under pump-action shotgun barrels.
Muzzle – The end of a firearms barrel from which the projectile exits when fired.
Muzzle Brake – A part fitted or integrated with the muzzle intended to counter recoil and/or muzzle flip via redirection of gasses following a gunshot.
Muzzle Climb / Flip – A recoil movement of a firearm that causes the muzzle end of a firearm to rise due to a pivotting action. A result of the weapon design and recoil energy distribution.
Muzzle Energy – The kinetic energy of a projectile as it clears the muzzle of a firearm. Basic physics, the faster and heaver the projectile, the more the energy and potential destructive power.
Muzzle Velocity – The velocity at which a projectile exits the muzzle of a firearm.
Out of Battery – The position of the parts and cartridge in a firearm action at any point OTHER than in firing position. Ignition of a cartridge when Out of Battery is extremely hazardous and generally causes catastrophic damage to the firearm and possible injuries to the shooter. As firearms are designed to avoid this, it’s commonly caused by a malfunction of one or more safety mechanisms, or use of incorrect/faulty ammunition.
Parkerization – A process of electrochemical conversion coating in order to add protection and corrosion resistance to a steel surface. Produces a natural matte black finish of the metal.
Picatinny Rail – A standardized mounting rail system added to many modern firearms that allows attachment of a variety of accessories such as optics, lights, and grip devices. A 1980’s standardization of the Weaver Rail system developed as an optics mounting system in the 1970’s. Also referred to asa MIL-STD-1913 rail, a tactical rail, or just a rail.
Plinking – Unstructured shooting exercise normally directed at random items as targets such as bottles, cans, watermelons, old appliances, etc., normally in an outdoor non-regulated shooting range setting.
Point-of-Aim – The point on which a firearm’s sights are aligned.
Point-of-Impact – The point at which a fired projectile strikes.
Rate of Fire – The rate at which a firearm is able to fire projectiles, most commonly given in “rounds per minute” (RPM).
Receiver – The main body of a firearm which contains the majority of it’s operative parts such as trigger mechanism.
Recoil – The energy that causes rearward momentum of a firearm when fired due to newton’s third law of motion. Also referred to as “kick.”
Recoil Operated (Recoil operated) – A variety of operation for autoloading firearms wherein the force of recoil is used to work the action of the firearm. Most common mode of operation for autoloading handguns and small caliber rifles.
Revolver – A firearm that uses a cylinder containing multiple chambers (most commonly five or six), allowing for repeated single or double action firing until all cartridges in the chambers have been fired.
Rifling – Spiral (helical) grooves cut into the bore of a firearm barrel which produces a spin to the projectile for the purposes of gyrostabilization of the bullet, allowing for much higher accuracy over range of smoothbore firearms. Generally, propellent gasses behind the projectile cause slight expansion of the bullet, forcing it to engage the rifling due to it’s expanded size.
Rimfire – A class of cartridges in which the rim contains priming compound, making the rim act as a percussion cap. In firearms designed for this cartridge, the firing pin strikes the rim rather than a center mounted primer.
Round – A cartridge. Multiple cartridges are often referred to as “rounds.”
Safety – A mechanism incorporated in the design of the firearm’s action which helps prevent unintended discharge of the firearm.
Select(ive) Fire – A class of firearm which allows for both semi-automatic operation and at least one mode of automatic fire (fully automatic and/or Burst fire), which can be changed by some type of selector mechanism. A pre-requisite feature for a firearm to be considered an Assault Rifle.
Semi-Automatic – A mode of automatic fire wherein one round is fired with each individual pull of the trigger.
Semi-Wadcutter (SWC) – A type of bullet whose design generally consists of a conical shape truncated with a flat tip. Offers better Ballistics, and easier feeding in automatic handguns, than a full Wadcutter, but still punches clean holes in paper / light material and gives most of the other advantages of a Wadcutter with less drawbacks.
Short-Barreled Rifle (SBR)/ Short-Barreled Shotgun (SBS) – A legal class of firearm in the United States (either rifle or shotgun, respectively) which are designed to be used with a shoulder stock but have a barrel length less than 16″, or overall length less than 26″, making them subject to the National Firearms Act of 1934 (NFA).
Single-Action – A mode of operation of a firearm’s trigger in which the hammer is cocked manually (or by action of a previous shot), and the trigger is used for the one purpose of releasing the hammer to fire the weapon. Most common in non-autoloading firearms and older revolvers, but also notably in some automatic handguns such as the M1911 and Browning Hi-Power, it’s advantage here being a short, potentially light, crisp trigger pull.
Slamfire – A potentially very dangerous unintended discharge by means of a cartridge being triggered as it’s loaded into the chamber (cartridge triggered as it’s being slammed into the chamber). Additionally, may occur out of battery increasing danger. Most commonly associated with using commercial or reloaded ammunition with military / military-style firearms that use free floating firing pins vs. spring loaded ones, as military spec ammunition tends to use harder primers that are not as easily triggered.
Slidebite – Similar to Hammer Bite, cut or abrasian to the shooter’s main hand due to the sharp rearward motion of an automatic handgun’s slide when one’s grip is too high. Common on smaller handguns with less of a tang at the top of the grip, remedied in handguns that use a beavertail tang as part of the grip.
Sling – A strap (sometimes a harness depending on style) which allows a firearm to be carried hands free. Different styles allow for simple transport, or for ease of readiness / transition to/from other weapons.
Snubnose – A revolver with a very short barrel length, typically under 3″.
Squib / Squib load – A cartridge malfunction in which the projectile doesn’t exit the firearm’s barrel, and becomes stuck. Very dangerous as it may not be immediately noticed, and a follow up shot will very likely damage the firearm, and could cause catastrophic failure and injury to the shooter or people nearby.
Stock – The part of a firearm to which the barrel and receiver are attached, which is held against the shoulder in firing, for means of stability and aim.
Submachine Gun – A type of fully automatic firearm designed to fire pistol cartridges.
Suppressor – A device that is attached to, or integrated with, a firearm’s barrel in order to reduce sound output and reduce muzzle flash visibility when firing.
Terminal Ballistics – The field of ballistics that involves the behavior of a projectile upon impact and entry into a target.
Trigger – The mechanism in a firearm which activates the firing sequence of a firearm’s action, most commonly a lever which releases the hammer or striker to hit the firing pin, triggering the cartridge.
Wadcutter – A type of bullet designed specifically for shooting paper or other thin, low-density targets, with a flat front, intended to cut a very clean, distinct hole in the target.
Wildcat Cartridge – A type of cartridge for which commerical ammunition and firearms are not mass-produced. Commonly designed for a singular purpose, and to maximize effectiveness to that end.
Windage – An adjustment of firearm sights side-to-side (as in to adjust for a crosswind). Adjustment of windage will adjust the point of impact horizontally.
Zeroing – Configuring the sights of a firearm (commonly a scope or other optics) so that the point of aim matches the point of impact at a specific range.