Firearms Related Terms, Initialisms, and Acronyms
AA - Anti-aircraft, also Accurate Arms - a modern gun powder manufacturer
ACP - Automatic Colt Pistol, a cartridge designation. e.g. .45ACP, .380ACP
AE - Action Express, angle eject, or American Eagle
AI - Ackley Improved
American Eagle - Federal Ammunition's practice ammunition brand.
AMP - Auto Mag Pistol
Anneal - To soften metal by heating it. Used to extend the useful reloading life of brass cartridge case necks by softening them; thus permitting more reloading operations to be performed before the work hardening effect of the cold, forced reshaping of the resizing operation causes metal fatigue/cracking in the neck area, making the brass case unusable for further reloading. Brass and copper are annealed by fast cooling, usually by quenching, from a heated condition. Steel is annealed by a slow cooling. Quenching of steel from high heat has the opposite effect from the same treatment of brass and copper.
Anticipating the Shot - An involuntary action which occurs immediately before/during the trigger break/firearm discharge. Also called flinching.
AP - Armor piercing
Aperture Sights - A type of iron sights in which the user aligns a front and rear sight by sighting through an aperture in the rear sight.
API - Armor piercing, incendiary
APT - Armor piercing, tracer
AR - Armalite Rifle, commonly mistaken to stand for Assault Rifle. e.g. AR15, AR10
BAR - Browning Automatic Rifle. Originally a fully automatic military weapon designed by John Browning and issued by the U.S. military but also later the name of a line of semi-automatic rifles marketed by the Browning firearms company.
Battery - The state of a firearm when the bolt/slide is fully forward (especially locked closed) with a round chambered.
Bearing Surface - The portion of a bullet which contacts the bore of the barrel as it travels from chamber to muzzle. Sufficient bearing surface is required for good accuracy.
BBWC - Bevel Base Wadcutter (bullet design)
BC - Ballistic coefficient: A measure of how aerodynamic a projectile is. Bullets with larger BCs are more aerodynamic and will lose velocity slower. It is an indexed measure of a bullet's ability to overcome aerodynamic resistance, in flight, relative to the performance of a standard "reference" projectile used to compute ballistics tables. Mathematically it is the ratio of bullet's SD to its coefficient of form, or the ratio of the bullet's weight to the product of the square of its diameter and its form factor (coefficient of form).
BCG - Bolt carrier group
Bedding - Material and/or methods used to precisely fit rifle action to a stock.
BHN - Brinnell hardness number
Birdshot - Shotgun pellets with small diameters, typically used to hunt birds or shoot clay targets. Also a shotgun cartridge loaded with such pellets. Technically any shotgun pellet diameter under 0.24" is birdshot, but in common practice the term generally refers to pellet diameters of around 0.1" and smaller.
Black Powder - The original gunpowder used before smokeless powder was invented. Black Powder burns with a distinctive smell, creating large quantities of white smoke and corrosive fouling. While it is black in color, so is modern smokeless powder.
Blowback - A semi-automatic/automatic action in which the action is held closed only by spring pressure and the inertia of the bolt/slide and is operated by the bolt/slide being blown open upon firing.
Bore - The inside of a firearm's barrel. Also an archaic measure of the size (diameter) of a barrel which describes the diameter of the barrel as being the diameter of a lead ball in which the number preceding the "bore" designation is equal to the number of lead balls of the barrel diameter which are required to make up a pound. This is an identical measurement to "gauge" but is more commonly used to refer to rifled barrels. e.g. An 8 bore rifle would have a muzzle diameter of 0.835" since 8 balls of pure lead with diameters of 0.835" make up one pound.
BMG - Browning machine gun
Bore sight - To align the sights (esp. optical sights) of a firearm to the bore. Accomplished by use of a bore-sighting device or by sighting through the barrel. Boresighting is used prior to sighting in a rifle using live fire because it eliminates gross discrepancies between the bore and the sighting device and simplifies/shortens the zeroing process. It is not a substitute for zeroing/sighting in a rifle.
BP - Black powder
BPCR - Black powder cartridge rifle
Breech - The portion of the firearm which the base of the cartridge rests against when chambered and during firing. The firing pin typically operates on the primer through a hole in the breech.
Brisance - the "shattering" effect of explosives; also, the burn rate, in terms of acceleration, i.e. how quickly is the maximum burn rate of an explosive mass reached?
Browning - John Moses Browning. A prolific gun designer who developed the tilting barrel, locked-breech, recoil operated semi-automatic pistol, as well as many other designs. Browning designed pistols, rifles, shotguns and machine guns. A number of his designs were fielded by the U.S. military and some are still in service over 90 years after his death. Also Browning firearms company, named for J.M. Browning. Also a firearm with the Browning brand.
BT - Boattail (rifle bullet design). Boattail bullets have a rebated/tapered base which improves aerodynamics.
Buckshot - Shotgun pellets with diameters of 0.24" or greater. Also a shotgun cartridge loaded with such pellets.
BUIS - Backup iron sights
Bullet - An elongated projectile (vs. a ball or pellet) which is expelled from a firearm's barrel (especially a rifled barrel) at firing.
Burn rate - The relative speed at which smokeless powders burn. This is determined by the size and shape of granules, amount and nature of any coatings and, in some cases, specific physical design of the granules, such as perforations, tubes, rods, ball (beads) or disk shapes (flattened beads).
C&R - Curio and Relic Firearms License. A federal firearms license which allows collectors to directly acquire (without the assistance of a conventionally FFL holder) a variety of firearms which qualify as collectible.
Cal. - Caliber (inches or millimeters); projectile (bullet) diameter or the diameter of some specifically defined point in the bore of a barrel; the nominal or approximate diameter of a bore expressed similarly. Commonly used to refer to a specific cartridge or chambering although, strictly speaking that is technically incorrect. e.g. A .45ACP caliber pistol. Caliber has a completely different meaning when applied to large naval guns.
Carbon Scoring - The black "burn marks" that appear around the barrel/cylinder gap on revolvers. These marks are most apparent on stainless steel or plated guns. They are harmless, but can generally be removed with mild abrasives if the shooter is concerned about them. However, abrasive removal techniques, should not be employed on revolvers with blued finishes or aluminum cylinders as damage can result.
Cant - A tilt, most often the tilt of a holster to aid in concealment or to speed the draw.
Cartridge - Completed assembly, comprised of a case (the central component), primer (for ignition), powder (primary energy source) and bullet (projectile). The cartridge is placed into the chamber and confined by some sort of breech device for firing.
CBTO - Cartridge base to ogive
CCW - Concealed carry weapon, also the license allowing legal concealed carry of a handgun
Centerfire - A cartridge with the primer contained in the center of the base ("head") of the cartridge. Also a firearm chambered for a centerfire caliber.
Chamber - The portion of a firearm which contains the cartridge at firing.
Chambering - The "caliber" or cartridge designation for a particular type of rifle or ammunition. i.e., "This rifle is available in the following chamberings: ..."; Specific machined dimensions to the interior rearmost portion of a barrel which results in a chamber that will accept and safely fire one cartridge design only, i.e., .30-'06 Springfield, .270 Winchester, .223 Remington, .38-55 Winchester-Ballard, .45-'70 Government, etc. Although acceptable chamber dimensions are defined and accepted throughout the firearms industry by the ANSI-approved SAAMI, there are many "wildcat" and "improved" variations of standard SAAMI chamberings in use. Also the act of introducing a cartridge to the chamber to ready a firearm for discharge.
Charge - Quantity of powder; usually in grains. Also the act of placing a powder charge in a chamber or cartridge. Less often the act of introducing a cartridge to the chamber of a firearm in preparation to fire it.
Choke - The taper in the last few inches of a shotgun barrel. This is usually a tightening of the bore to a slightly smaller diameter from the actual gauge measurement of the barrel. Some typical shotgun choke names, from least to most taper, are: cylinder (no taper), improved cylinder (or simply: "improved"), modified cylinder ("modified") and full choke ("full"). This is not a complete list, but typical. Some rimfire rifles and airguns with rifled bores are choked at the muzzle, but this is not common.
CIP - The European standards organization analogous to the U.S. SAAMI organization. The groups translated name is Permanent International Commission
CLASS III - Refers to the Class III FFL required to deal in NFA items (full-auto, suppressors, etc.)
Clip - A strip of metal that is used to hold cartridges together to facilitate the loading into (usually) an internal rifle magazine. Sometimes used carelessly or as slang to refer to a magazine.
Cocked & Locked - Condition 1
COL or COAL - Cartridge overall length - (same as OAL)
Condition 1 - Pistol: Full magazine, cartridge in chamber, hammer cocked, safety on. AKA "cocked and locked."
Condition 2 - Pistol: Full magazine, cartridge in chamber, hammer down, safety off.
Condition 3 - Pistol: Full magazine, chamber empty.
Condition 4 - Pistol: Full magazine separate from gun, chamber empty.
Components (reloading) - Individual components that make up the "recipe" for a hand loaded cartridge. The four components are: primer, case, bullet and powder.
Cooper - Colonel John (Jeff) Cooper. Considered to be the father of the Modern Handgun Technique, Cooper wrote extensively in periodicals and in published books about shooting, self-defense, tactics and hunting.
Corrosive ammunition - The original priming compound used with modern smokeless powder was corrosive, necessitating special and rigorous cleaning to prevent damage to firearms. Corrosive primed ammunition is rare today, although some corrosive surplus may still be available. New ammunition is invariably non-corrosive.
Crown - The transistion between the bore and the muzzle. Generally it consists of a small bevel between the two, but may also be a very sharp transition. It is critical to accuracy and therefore damage/wear to the crown should be avoided if at all possible. This is the reason for the common recommendation to clean from the breech to avoid having the cleaning rod rub against the crown.
Cruiser Ready - Shotgun: Full magazine, chamber empty, hammer down, safety off.
CUP - Copper units of pressure; a method of measuring chamber pressure. CUP measurements are becoming obsolete with PSI measurements being the new standard.
Cylinder Gap - The distance between the front of the cylinder and the rear of the barrel in a revolver.
DA - double action, as opposed to single action (SA), DA cocks the hammer (and in some cases positions a cartridge) and then fires the gun all with a single pull, through full travel, of the trigger
DAO - Double action only. A firearm which operates as a double-action but in which there is no provision to cock the hammer/striker and operate the trigger in single-action mode.
Delayed Blowback - A semi-automatic action in which the action is held closed only by spring pressure and the inertia of the bolt/slide and is operated by the bolt/slide being blown open upon firing but with some additional delaying influence/mechanism slowing/delaying the opening process.
DEWC - Double ended wadcutter (bullet design)
Dryfire - Following the necessary steps to discharge a firearm but with the chamber unloaded. A common and valuable practice technique. Also a common way that firearms are unintentionally discharged. Dryfire practice should be conducted with a strong dedication to safety given how strongly unintentional discharges are associated with the practice.
EAA - European American Arms, a manufacturer of firearms
Elevation - Vertical deflection on the target or of the sights.
Energy - Kinetic Energy. A scientific quantity (measured in ft-lbs or Joules) that relates to the potential of a moving object to do "work". It is commonly used as a metric for comparing various cartridges/loadings and also as a marketing tool by ammunition companies.
FA - Fully automatic, a design which fires continually if the trigger is held to the rear. A machine gun.
FC - Federal Cartridge
FCD - Factory crimp die
FL - Full length die
Flinch - An involuntary action which occurs immediately before/during the trigger break/firearm discharge.
FMJ - Full metal jacket (bullet design) where a lead core is enclosed by a copper, gilding metal or steel jacket but typically with the lead base exposed
FN - There are several arms factories in different countries which use the initials "FN", standing roughly for National Factory. The best known FN is the Belgian arms manufacturer, Fabrique Nationale d'Armes d'Guerre or National Factory of War Arms, in Leige and Herstal, Belgium.FN was the developer of the Fusil Automatique Leger or Light Automatic Rifle, commonly called the FAL or FN-FAL. FALs are or have been the standard service rifle of a number of countries, including most of the British commonwealth, and were manufactured in several countries. Several semi-auto only versions are available on the U.S. market. Also: flat nose (bullet design)
Follow Through - Continuing to do whatever was happening when the shot broke. In shotgunning, this means continuing the swing even after the shot has fired. In target shooting, this generally means continuing to hold the gun steady and normally after the shot fires.
FOPA - Firearms Owner Protection Act of 1986. The FOPA relaxed many onerous restrictions imposed by the GCA but included a "poison pill" called the Hughes amendment which closed the registry for machineguns, effectively limiting the number of transferrable machineguns in the U.S. from that point forward.
Forcing Cone - The rearmost portion of a revolver barrel where the bullet makes the jump from the cylinder, through the cylinder gap and into the barrel. Typically smooth/unrifled initially, it tapers down and the rifling begins within a few mm.
Four Rules - Rules of firearm safety per Cooper. 1) All guns are always loaded. Even if they are not, treat them as if they are. 2) Never let the muzzle cover anything you are not willing to destroy. 3)Keep your finger off the trigger until your sights are on the target. 4)Identify your target, and what is behind it.
FP - Flat point (bullet design), also firing pin
FPS - Feet per second, also firing pin safety
FTE - An ambiguous acronym referring to either a failure to eject or a failure to extract.
FTF - An ambiguous acronym referring to either a failure to feed or a failure to fire (a misfire).
G&A - Guns & Ammo (print magazine)
GA - Gauge (also: ga.) a measure of the size (diameter) of a barrel which describes the diameter of the barrel as being the diameter of a lead ball in which the number preceding the "gauge" designation is equal to the number of lead balls of the barrel diameter which are required to make up a pound. This is an identical measurement to "bore" but is more commonly used to refer to smoothbore/shotgun barrels. e.g. A 12 gauge shotgun would have a muzzle diameter of 0.73" since 12 balls of pure lead with diameters of 0.73" would make up one pound.
GAP - Glock Automatic Pistol. A cartridge designation. e.g. .45GAP
Gas Operated - A semi-automatic/automatic action in which the action is locked closed until gas tapped from the bore initiates an unlocking action which separates the barrel and the breech.
GCA - Gun Control Act of 1968. The GCA of 1968 implemented the federal licensing requirements for firearms dealers as well as restrictions on shipping/mailing firearms and on interstate transfers of firearms.
GC - Gas check; a copper-zinc alloy cup used as gilding to protect the base of lead bullets from hot gas obduration during internal ballistics. Gas checks also tend to reduce lead buildup in the bore.
GFL - Headstamp on Fiocchi ammunition.
Grain - An otherwise obsolete/archaic measure of weight remaining in use only as a measure the weight of bullets, powder charges and a few other firearms-related quantities. There are 7,000 grains to a pound, 437.5 grains to an ounce, 15432.4 grains to the kilogram and 15.4grains to the gram.
Groove - The depressed portion of rifling.
H&R - Harrington & Richardson, a manufacturer of firearms
Handgun - A firearm designed so that it can be fired with one hand without holding it to the shoulder. Generally small compared to rifles or shotguns. The NFA act requires that handguns have rifled barrels unless they are registered properly.
HBWC - Hollow base wad cutter (bullet design)
HD - Home Defense
Headspace - The measurement between two points in a chamber which are the confining boundaries of cartridge movement during chambering and firing. Insufficient headspace hinders complete chambering of the cartridge. Excessive headspace permits case stretching and can permit case separation, which will result in high pressure gas leakage during the firing/pressure cycle. Gas leakage can be very dangerous and may cause damage to equipment and injury to the shooter. Headspace is defined and measured differently for each case design. Rimless, rimmed and belted bottleneck cases each have a method unique to the design and a measurement specific to the chambering. Straight walled cases, rimless and rimmed, also have unique methods and cartridge-specific measurements.
Headstamp - Identifying markings/stampings on the base ("head) of a metallic cartridge. The caliber and maker are virtually always identified and there may be additional information such as a date of manufacture.
Heller - A court case (District of Columbia v. Joseph Heller) which was heard by the Supreme Court and resulted in a ruling affirming that the Second Amendment protects an individual's right to possess a firearm independent of membership or service in a militia and that such firearms may be used for self-defense/home defense or other lawful purposes. In particular, the ruling found that Washington, D.C.'s ban on handguns and the restrictions requiring that rifles and shotgun must be kept trigger locked or unloaded and disassembled were unconstitutional.
Hodgdon - A modern gun powder manufacturer
HP - Hollow point (bullet design)
HRC - Rockwell Hardness C Scale. Sometimes written RC.
IMR - Modern gun powder manufacturer: Improved Military Rifle; formerly DuPont
Iron Sights - Any sighting system based on a sight system which does not include sighting optics or gun mounted optical devices.
IWB - Inside the WaistBand. A type of holster which fits inside the waistband of the pants instead of outside the pants. Used for concealment.
Jag - A pointed and ridged, caliber specific, cleaning attachment which typically screws onto a cleaning rod and is used to push patches through the bore.
JHC - Jacketed hollow cavity (bullet design)
JFP - Jacketed flat point (bullet design)
JHP - Jacketed hollow point (bullet design)
JMB or J.M.B. - John Moses Browning. See 'Browning'. A prolific American firearms designer.
KE - Kinetic Energy. See 'Energy'
Keith - Elmer Keith. Keith wrote prolifically for periodicals and also published a number of books on various firearm-related topics, including hunting, revolver shooting and reloading. His reloading efforts with the .44 Special led to the development of the .44Magnum.
KYPD - Keep your powder dry
Land - The raised portion of rifling.
Leade - The portion of the bore forward of the chamber, where the rifling begins.
Locked Breech, Recoil Operated - A semi-automatic/automatic action in which the action is locked closed until recoil has moved the locked barrel/breech sufficiently to initiate an unlocking action which separates the barrel and the breech.
Long Gun - A shoulder-stocked firearm. Not a pistol/handgun.
LOS - Line of sight
LPP - Large pistol primer
LRN - Lead round nose (bullet design)
LRP - Large rifle primer
LSWC - Lead semi-wad cutter (bullet design)
LWC - Lead wad cutter (bullet design)
Mag. - Magazine or magnum.
Magazine - Ammunition holders (either integral to a firearm or detachable) that are typically equipped with a spring to move the stored ammo into position for feeding. Sometimes referred to carelessly or using slang as 'clips'.
MAP - Maximum Average Pressure, a term used by SAAMI to indicate "the recommended maximum pressure level for loading a particular type of commercial ammunition."
McDonald - A court case (McDonald v, City of Chicago) which was heard by the Supreme Court and resulted in a ruling that the Second Amendment's protection of the individual right to own and use firearms for lawful purposes (per the earlier Heller ruling) must be respected by state and local governments, not just by federal law.
MIM - Metal Injection Molding. A process involving the creation of parts in forms from metal powder. It results in tight dimensions on the finished part without the need for final machining and is therefore very attractive to manufacturers. Commonly considered to be a cost-cutting measure by the firearms community and therefore undesirable.
MM - Millimeters; also mm
MV - Muzzle velocity, usually in fps, but also in meters per second in most of Europe. Velocity of the bullet at or very near the muzzle of the barrel
MOA - Minute of angle. Degrees are broken down into minutes and seconds, just as hours are. There are 60 minutes in a degree and 60 seconds in a minute. If the muzzle of the rifle is placed at the center of an imaginary circle with the target on the circumference of the circle, then the distance between impacts on a target can be measured as distances on the circle using angles. 1 Minute of angle at 100 yards is approximately 1.047", usually simplified to 1". Similarly, 1 MOA at 25 yards corresponds to about 0.25" and to about 5" at 500 yards.
Momentum - A scientific quantity that relates to how difficult it is to stop a moving object. The Power Factor calculation used to classify cartridges in some pistol competitions is a scaled version of momentum.
Muzzle - The front portion of the barrel surrounding the hole where the bullet exits. Also to point a gun at someone, generally unintentionally.
NAA - North American Arms, a manufacturer of firearms
NEF - New England Firearms, a manufacturer of firearms
NFA - National Firearms Act (1934). The NFA, among other things implemented the federal requirement for registration of machineguns, silencers, and short barreled long guns.
NRR - Noise Reduction Rating. The amount hearing protection will reduce the noise power reaching the shooter's ears. Expressed in decibels (dB). Larger numbers mean more noise reduction.
O/U - Over/under (shotgun)
OAL - Overall length - usually refers to the length of a complete cartridge (same as COAL or COL)
Ogive - The curved portion of a bullet ahead of the cylindrical portion or shank. The radius of the ogive is usually expressed in multiples or fractions of the caliber. (pronounced oh-jive)
Open Sights - A type of iron sights in which the user aligns a front and rear sight without sighting through an aperture, usually by placing a post front sight in the notch of the rear sight.
OWB - Outside the WaistBand. A type of holster which is designed to be worn outside the waistband of the pants.
PBR - Point blank range, used to refer to either very close range shooting (e.g.He was shot at point blank range) or to shooting within the range at which a rifle's trajectory does not exceed the size of the desired target and therefore there is no need to adjust the point of aim or the sights and the shooter may simply hold on the center of the target. (e.g. With a 120gr bullet, this rifle's point blank range on an 8" target is 305 yards).
PDW - Personal Defense Weapon
PFL - Partial full length die
Pistol - Handgun. In modern times, the term 'pistol' is sometimes used to refer exclusively to handguns which are not revolvers, but this is not a universally accepted convention.
POA - Point of aim.
POI - Point of impact.
Points - Per BATF's interpretation of the GCA of 1968, handguns must score above a certain arbitrary threshold on a points scheme where points are awarded based on a set of rules supposedly designed to prevent the import of low quality and/or non-sporting handguns.
Polygonal Rifling - A rifling system consisting of a bore shaped like a polygon rather than having distinct lands and grooves. Employed by Kahr, Glock and H&K, among others. Commonly either hexagonal rifling (6 sided polygon) or octagonal rifling (8 sided polygon).
PPC - A cartridge designed in 1974 by Dr. Louis Palmisano and Ferris Pindell. Based on the 220 Russian case with a head diameter of .441 - .445. Considered to be the most efficient cartridge design available, the .22 cal PPC and 6mm PPC virtually dominated benchrest accuracy competition for many years.
Primer - A small explosive charge that fires upon impact from the firing pin and provides the energy/heat to ignite the powder charge. A primer may be self-contained in a metal cap that fits into the center of the base ("head") of a centerfire cartridge or may be contained in the hollow rim of a rimfire cartridge base.
PSI - Pounds per square inch; also: psi. This is the normally accepted measure of pressure exerted on the inside wall of the chamber of a modern rifle or handgun during the firing cycle. In times past, pressure was measured in CUP but PSI is a more accurate pressure measurement and requires less complicated measuring equipment. PSI is replacing the use of CUP as a standard reference of pressure in all firearms testing and pressure proofing.
RC - Rockwell Hardness C Scale. Sometimes written HRC.
Revolver - A type of handgun/pistol with a revolving cylinder containing multiple chambers. The chambers can be fired, in turn, by either pulling the trigger (double action) or by cocking the hammer and pulling the trigger (single action). There have also been a very few "automatic revolvers" where the recoil of the gun advanced the cylinder.
Repeater - Any firearm which can fire more than one shot without being reloaded. i.e. Not a single shot firearm.
Rifle - A long gun with a rifled bore, designed to be fired from the shoulder.
Rimfire - A cartridge with the primer contained in the hollow rim of the base ("head") of the cartridge. Also a firearm chambered for a rimfire caliber.
RN - Round nose (bullet design)
S&W - Smith & Wesson
SA - Single action, as opposed to double action (DA), SA releases the hammer/striker for primer contact and firing AFTER cocking of the hammer/striker and positioning of the cartridge for firing is accomplished by means other than pulling the trigger. Also less commonly, Semi-Automatic.
SAA - Single Action Army; a famous design of revolver by Colt used in early America and credited with finalizing the popularity of mass produced, brass cartridge handguns. This is the cowboy revolver of Hollywood Western Motion Pictures.
SAAMI - Sporting Arms and Ammunition Manufacturers Institute; an accredited standards developer for the American National Standards Institute (ANSI)
SAF - Second Amendment Foundation
SAO - Single action only
SB - Small base die
SBR - Short Barrel Rifle. The NFA of 1934 places a minimum length on the barrel of a gun with a rifled barrel and a shoulder stock. Any shoulder stocked firearm with a rifled barrel which does not meet the barrel length limit is an SBR and must be registered per NRA restrictions.
SBS - Short Barrel Shotgun. The NFA of 1934 places a minimum barrel length on a gun with a smoothbore and a shoulder stock. Any shoulder stocked firearm with a smooth bore which does not meet the barrel length limit is an SBS and must be registered per NRA restrictions.
SD - Self Defense. Also sectional density; ratio of bullet's weight, in pounds, to its cross-sectional area, in inches.
Select Fire - Also Selective Fire. A firearm which can operate either as a semi-automatic or as a fully automatic/burst fire weapon depending on the setting of a selector switch.
Semi-automatic - A firearm which performs the actions of firing, extraction/ejection of the empty case, loading of a new round from the magazine and, if necessary, cocking, each time the trigger is pulled. A semi-automatic firearm will fire one shot per trigger pull until the magazine is empty. Also referred to as 'autoloading', 'self-loading' or, less accurately, as 'automatic'.
Shotgun - A long gun with a smooth bore, designed to be fired from the shoulder.
SJHP - Semi-jacketed hollow point
SKS - Samozaryadnaya Karabina Simonova, or Self-loading carbine Simonov. Sergei Gavrilovich Simonov was one of the old Soviet Union's foremost arms designers. The rifle was adopted by the USSR in 1945, and was made both there and in China.
SLR - Self loading rifle
Slug - Most commonly used to refer to a solid projectile close to bore diameter (vs. one of many pellets much smaller than bore diameter) that is fired out of a shotgun. Also sometimes used as a synonym for 'bullet'. Also, the unit of mass in the United States Customary measurement system.
SMG - Sub-machine gun. A compact full-auto weapon typically chambered for a pistol cartridge.
SP - Soft point (a bullet design)
SPP - Small pistol primer
SRP - Small rifle primer
Standard Conditions - Ballistic Coefficient values are based on standard conditions of 59 degrees Fahrenheit and 29.53mm of mercury. For precise results, BC figures should be adjusted based on actual temperature and pressure measurements taken at the time of firing.
Sturm Ruger - Ruger Firearms. Alexander Sturm was a co-founder of Ruger and a good friend of William Batterman Ruger. He provided startup capital and also designed the Ruger eagle trademark. When Sturm died at the age of 28, Ruger changed the color of the Ruger eagle trademark from red to black.
Striker - A "spring-powered" firing pin. Rather than being struck by a hammer, a striker is released by the trigger/sear and driven forward by spring pressure to hit the primer.
SWC - Semi wadcutter (a bullet design), semi-wadcutters typically have a truncated cone nose but a sharp shoulder of full diameter. These bullets cut full diameter holes in targets but are more aerodynamic than full wadcutters and are more of a general purpose bullet than a full wadcutter
TC - Truncated cone (a bullet design)
Throat - Leade, freebore. The portion of the barrel immediately forward of the chamber. In some rifle chamber designs, the throat may be long and may transition into a relatively slow taper to full depth of lands and grooves (rifling). In other rifle designs the throat is relatively short and the transition to full depth rifling is abrupt, although all barrels have some taper from throat to full depth rifling. The immediate effect of the two extremes in design is to determine the maximum distance a bullet may protrude out the front of the case. This determines the final overall length of the loaded cartridge, for a given bullet shape.
Timing - A term that describes the proper function of a revolver. A number of processes must take place in the proper order during process of advancing the cylinder, locking it in place and cocking the hammer. If those process are not taking place as they should the revolver may be said to have "gone out of time".
TMJ - Total metal jacket (a bullet design) similar to full metal jacket, but with the base of the bullet also enclosed by the jacket.
Trajectory - The path traveled by the projectile as it moves from the muzzle of the firearm to the target. The trajectory is determined primarily by the angle of the bore, the initial projectile velocity, gravity, by wind and by air resistance although there are other less significant factors involved.
WBY - Weatherby
WC - Wad cutter (a bullet design), wad cutters have flat noses and sharp shoulders. Wadcutters cut neat, full diameter holes in targets which facilitates scoring.
Windage - Horizontal deflection on the target or of the sights.
Wind Value - A simple scaling factor used to determine the effect of wind on bullet deflection. If the wind is at more or less right angles to the direction of bullet travel, it is considered to be a full value wind. At about 30 degrees of angle to the direction of bullet travel it would be called a half value wind.
WWB - Winchester White Box. Winchester USA marked ammunition. Common budget practice ammunition, often bulk packed and available in common rifle and pistol calibers.
USRAC - U.S. Repeating Arms Company; firearms, ammo and reloading component manufacturer
Zero - The sight setting which puts a bullet at the point of aim at a given distance. e.g. The rifle has a 100 yard zero. Also the process of adjusting the sights to achieve a point of aim/point of impact correspondence at a desired distance. e.g. I need to zero my rifle.
ACP - Automatic Colt Pistol, a cartridge designation. e.g. .45ACP, .380ACP
AE - Action Express, angle eject, or American Eagle
AI - Ackley Improved
American Eagle - Federal Ammunition's practice ammunition brand.
AMP - Auto Mag Pistol
Anneal - To soften metal by heating it. Used to extend the useful reloading life of brass cartridge case necks by softening them; thus permitting more reloading operations to be performed before the work hardening effect of the cold, forced reshaping of the resizing operation causes metal fatigue/cracking in the neck area, making the brass case unusable for further reloading. Brass and copper are annealed by fast cooling, usually by quenching, from a heated condition. Steel is annealed by a slow cooling. Quenching of steel from high heat has the opposite effect from the same treatment of brass and copper.
Anticipating the Shot - An involuntary action which occurs immediately before/during the trigger break/firearm discharge. Also called flinching.
AP - Armor piercing
Aperture Sights - A type of iron sights in which the user aligns a front and rear sight by sighting through an aperture in the rear sight.
API - Armor piercing, incendiary
APT - Armor piercing, tracer
AR - Armalite Rifle, commonly mistaken to stand for Assault Rifle. e.g. AR15, AR10
BAR - Browning Automatic Rifle. Originally a fully automatic military weapon designed by John Browning and issued by the U.S. military but also later the name of a line of semi-automatic rifles marketed by the Browning firearms company.
Battery - The state of a firearm when the bolt/slide is fully forward (especially locked closed) with a round chambered.
Bearing Surface - The portion of a bullet which contacts the bore of the barrel as it travels from chamber to muzzle. Sufficient bearing surface is required for good accuracy.
BBWC - Bevel Base Wadcutter (bullet design)
BC - Ballistic coefficient: A measure of how aerodynamic a projectile is. Bullets with larger BCs are more aerodynamic and will lose velocity slower. It is an indexed measure of a bullet's ability to overcome aerodynamic resistance, in flight, relative to the performance of a standard "reference" projectile used to compute ballistics tables. Mathematically it is the ratio of bullet's SD to its coefficient of form, or the ratio of the bullet's weight to the product of the square of its diameter and its form factor (coefficient of form).
BCG - Bolt carrier group
Bedding - Material and/or methods used to precisely fit rifle action to a stock.
BHN - Brinnell hardness number
Birdshot - Shotgun pellets with small diameters, typically used to hunt birds or shoot clay targets. Also a shotgun cartridge loaded with such pellets. Technically any shotgun pellet diameter under 0.24" is birdshot, but in common practice the term generally refers to pellet diameters of around 0.1" and smaller.
Black Powder - The original gunpowder used before smokeless powder was invented. Black Powder burns with a distinctive smell, creating large quantities of white smoke and corrosive fouling. While it is black in color, so is modern smokeless powder.
Blowback - A semi-automatic/automatic action in which the action is held closed only by spring pressure and the inertia of the bolt/slide and is operated by the bolt/slide being blown open upon firing.
Bore - The inside of a firearm's barrel. Also an archaic measure of the size (diameter) of a barrel which describes the diameter of the barrel as being the diameter of a lead ball in which the number preceding the "bore" designation is equal to the number of lead balls of the barrel diameter which are required to make up a pound. This is an identical measurement to "gauge" but is more commonly used to refer to rifled barrels. e.g. An 8 bore rifle would have a muzzle diameter of 0.835" since 8 balls of pure lead with diameters of 0.835" make up one pound.
BMG - Browning machine gun
Bore sight - To align the sights (esp. optical sights) of a firearm to the bore. Accomplished by use of a bore-sighting device or by sighting through the barrel. Boresighting is used prior to sighting in a rifle using live fire because it eliminates gross discrepancies between the bore and the sighting device and simplifies/shortens the zeroing process. It is not a substitute for zeroing/sighting in a rifle.
BP - Black powder
BPCR - Black powder cartridge rifle
Breech - The portion of the firearm which the base of the cartridge rests against when chambered and during firing. The firing pin typically operates on the primer through a hole in the breech.
Brisance - the "shattering" effect of explosives; also, the burn rate, in terms of acceleration, i.e. how quickly is the maximum burn rate of an explosive mass reached?
Browning - John Moses Browning. A prolific gun designer who developed the tilting barrel, locked-breech, recoil operated semi-automatic pistol, as well as many other designs. Browning designed pistols, rifles, shotguns and machine guns. A number of his designs were fielded by the U.S. military and some are still in service over 90 years after his death. Also Browning firearms company, named for J.M. Browning. Also a firearm with the Browning brand.
BT - Boattail (rifle bullet design). Boattail bullets have a rebated/tapered base which improves aerodynamics.
Buckshot - Shotgun pellets with diameters of 0.24" or greater. Also a shotgun cartridge loaded with such pellets.
BUIS - Backup iron sights
Bullet - An elongated projectile (vs. a ball or pellet) which is expelled from a firearm's barrel (especially a rifled barrel) at firing.
Burn rate - The relative speed at which smokeless powders burn. This is determined by the size and shape of granules, amount and nature of any coatings and, in some cases, specific physical design of the granules, such as perforations, tubes, rods, ball (beads) or disk shapes (flattened beads).
C&R - Curio and Relic Firearms License. A federal firearms license which allows collectors to directly acquire (without the assistance of a conventionally FFL holder) a variety of firearms which qualify as collectible.
Cal. - Caliber (inches or millimeters); projectile (bullet) diameter or the diameter of some specifically defined point in the bore of a barrel; the nominal or approximate diameter of a bore expressed similarly. Commonly used to refer to a specific cartridge or chambering although, strictly speaking that is technically incorrect. e.g. A .45ACP caliber pistol. Caliber has a completely different meaning when applied to large naval guns.
Carbon Scoring - The black "burn marks" that appear around the barrel/cylinder gap on revolvers. These marks are most apparent on stainless steel or plated guns. They are harmless, but can generally be removed with mild abrasives if the shooter is concerned about them. However, abrasive removal techniques, should not be employed on revolvers with blued finishes or aluminum cylinders as damage can result.
Cant - A tilt, most often the tilt of a holster to aid in concealment or to speed the draw.
Cartridge - Completed assembly, comprised of a case (the central component), primer (for ignition), powder (primary energy source) and bullet (projectile). The cartridge is placed into the chamber and confined by some sort of breech device for firing.
CBTO - Cartridge base to ogive
CCW - Concealed carry weapon, also the license allowing legal concealed carry of a handgun
Centerfire - A cartridge with the primer contained in the center of the base ("head") of the cartridge. Also a firearm chambered for a centerfire caliber.
Chamber - The portion of a firearm which contains the cartridge at firing.
Chambering - The "caliber" or cartridge designation for a particular type of rifle or ammunition. i.e., "This rifle is available in the following chamberings: ..."; Specific machined dimensions to the interior rearmost portion of a barrel which results in a chamber that will accept and safely fire one cartridge design only, i.e., .30-'06 Springfield, .270 Winchester, .223 Remington, .38-55 Winchester-Ballard, .45-'70 Government, etc. Although acceptable chamber dimensions are defined and accepted throughout the firearms industry by the ANSI-approved SAAMI, there are many "wildcat" and "improved" variations of standard SAAMI chamberings in use. Also the act of introducing a cartridge to the chamber to ready a firearm for discharge.
Charge - Quantity of powder; usually in grains. Also the act of placing a powder charge in a chamber or cartridge. Less often the act of introducing a cartridge to the chamber of a firearm in preparation to fire it.
Choke - The taper in the last few inches of a shotgun barrel. This is usually a tightening of the bore to a slightly smaller diameter from the actual gauge measurement of the barrel. Some typical shotgun choke names, from least to most taper, are: cylinder (no taper), improved cylinder (or simply: "improved"), modified cylinder ("modified") and full choke ("full"). This is not a complete list, but typical. Some rimfire rifles and airguns with rifled bores are choked at the muzzle, but this is not common.
CIP - The European standards organization analogous to the U.S. SAAMI organization. The groups translated name is Permanent International Commission
CLASS III - Refers to the Class III FFL required to deal in NFA items (full-auto, suppressors, etc.)
Clip - A strip of metal that is used to hold cartridges together to facilitate the loading into (usually) an internal rifle magazine. Sometimes used carelessly or as slang to refer to a magazine.
Cocked & Locked - Condition 1
COL or COAL - Cartridge overall length - (same as OAL)
Condition 1 - Pistol: Full magazine, cartridge in chamber, hammer cocked, safety on. AKA "cocked and locked."
Condition 2 - Pistol: Full magazine, cartridge in chamber, hammer down, safety off.
Condition 3 - Pistol: Full magazine, chamber empty.
Condition 4 - Pistol: Full magazine separate from gun, chamber empty.
Components (reloading) - Individual components that make up the "recipe" for a hand loaded cartridge. The four components are: primer, case, bullet and powder.
Cooper - Colonel John (Jeff) Cooper. Considered to be the father of the Modern Handgun Technique, Cooper wrote extensively in periodicals and in published books about shooting, self-defense, tactics and hunting.
Corrosive ammunition - The original priming compound used with modern smokeless powder was corrosive, necessitating special and rigorous cleaning to prevent damage to firearms. Corrosive primed ammunition is rare today, although some corrosive surplus may still be available. New ammunition is invariably non-corrosive.
Crown - The transistion between the bore and the muzzle. Generally it consists of a small bevel between the two, but may also be a very sharp transition. It is critical to accuracy and therefore damage/wear to the crown should be avoided if at all possible. This is the reason for the common recommendation to clean from the breech to avoid having the cleaning rod rub against the crown.
Cruiser Ready - Shotgun: Full magazine, chamber empty, hammer down, safety off.
CUP - Copper units of pressure; a method of measuring chamber pressure. CUP measurements are becoming obsolete with PSI measurements being the new standard.
Cylinder Gap - The distance between the front of the cylinder and the rear of the barrel in a revolver.
DA - double action, as opposed to single action (SA), DA cocks the hammer (and in some cases positions a cartridge) and then fires the gun all with a single pull, through full travel, of the trigger
DAO - Double action only. A firearm which operates as a double-action but in which there is no provision to cock the hammer/striker and operate the trigger in single-action mode.
Delayed Blowback - A semi-automatic action in which the action is held closed only by spring pressure and the inertia of the bolt/slide and is operated by the bolt/slide being blown open upon firing but with some additional delaying influence/mechanism slowing/delaying the opening process.
DEWC - Double ended wadcutter (bullet design)
Dryfire - Following the necessary steps to discharge a firearm but with the chamber unloaded. A common and valuable practice technique. Also a common way that firearms are unintentionally discharged. Dryfire practice should be conducted with a strong dedication to safety given how strongly unintentional discharges are associated with the practice.
EAA - European American Arms, a manufacturer of firearms
Elevation - Vertical deflection on the target or of the sights.
Energy - Kinetic Energy. A scientific quantity (measured in ft-lbs or Joules) that relates to the potential of a moving object to do "work". It is commonly used as a metric for comparing various cartridges/loadings and also as a marketing tool by ammunition companies.
FA - Fully automatic, a design which fires continually if the trigger is held to the rear. A machine gun.
FC - Federal Cartridge
FCD - Factory crimp die
FL - Full length die
Flinch - An involuntary action which occurs immediately before/during the trigger break/firearm discharge.
FMJ - Full metal jacket (bullet design) where a lead core is enclosed by a copper, gilding metal or steel jacket but typically with the lead base exposed
FN - There are several arms factories in different countries which use the initials "FN", standing roughly for National Factory. The best known FN is the Belgian arms manufacturer, Fabrique Nationale d'Armes d'Guerre or National Factory of War Arms, in Leige and Herstal, Belgium.FN was the developer of the Fusil Automatique Leger or Light Automatic Rifle, commonly called the FAL or FN-FAL. FALs are or have been the standard service rifle of a number of countries, including most of the British commonwealth, and were manufactured in several countries. Several semi-auto only versions are available on the U.S. market. Also: flat nose (bullet design)
Follow Through - Continuing to do whatever was happening when the shot broke. In shotgunning, this means continuing the swing even after the shot has fired. In target shooting, this generally means continuing to hold the gun steady and normally after the shot fires.
FOPA - Firearms Owner Protection Act of 1986. The FOPA relaxed many onerous restrictions imposed by the GCA but included a "poison pill" called the Hughes amendment which closed the registry for machineguns, effectively limiting the number of transferrable machineguns in the U.S. from that point forward.
Forcing Cone - The rearmost portion of a revolver barrel where the bullet makes the jump from the cylinder, through the cylinder gap and into the barrel. Typically smooth/unrifled initially, it tapers down and the rifling begins within a few mm.
Four Rules - Rules of firearm safety per Cooper. 1) All guns are always loaded. Even if they are not, treat them as if they are. 2) Never let the muzzle cover anything you are not willing to destroy. 3)Keep your finger off the trigger until your sights are on the target. 4)Identify your target, and what is behind it.
FP - Flat point (bullet design), also firing pin
FPS - Feet per second, also firing pin safety
FTE - An ambiguous acronym referring to either a failure to eject or a failure to extract.
FTF - An ambiguous acronym referring to either a failure to feed or a failure to fire (a misfire).
G&A - Guns & Ammo (print magazine)
GA - Gauge (also: ga.) a measure of the size (diameter) of a barrel which describes the diameter of the barrel as being the diameter of a lead ball in which the number preceding the "gauge" designation is equal to the number of lead balls of the barrel diameter which are required to make up a pound. This is an identical measurement to "bore" but is more commonly used to refer to smoothbore/shotgun barrels. e.g. A 12 gauge shotgun would have a muzzle diameter of 0.73" since 12 balls of pure lead with diameters of 0.73" would make up one pound.
GAP - Glock Automatic Pistol. A cartridge designation. e.g. .45GAP
Gas Operated - A semi-automatic/automatic action in which the action is locked closed until gas tapped from the bore initiates an unlocking action which separates the barrel and the breech.
GCA - Gun Control Act of 1968. The GCA of 1968 implemented the federal licensing requirements for firearms dealers as well as restrictions on shipping/mailing firearms and on interstate transfers of firearms.
GC - Gas check; a copper-zinc alloy cup used as gilding to protect the base of lead bullets from hot gas obduration during internal ballistics. Gas checks also tend to reduce lead buildup in the bore.
GFL - Headstamp on Fiocchi ammunition.
Grain - An otherwise obsolete/archaic measure of weight remaining in use only as a measure the weight of bullets, powder charges and a few other firearms-related quantities. There are 7,000 grains to a pound, 437.5 grains to an ounce, 15432.4 grains to the kilogram and 15.4grains to the gram.
Groove - The depressed portion of rifling.
H&R - Harrington & Richardson, a manufacturer of firearms
Handgun - A firearm designed so that it can be fired with one hand without holding it to the shoulder. Generally small compared to rifles or shotguns. The NFA act requires that handguns have rifled barrels unless they are registered properly.
HBWC - Hollow base wad cutter (bullet design)
HD - Home Defense
Headspace - The measurement between two points in a chamber which are the confining boundaries of cartridge movement during chambering and firing. Insufficient headspace hinders complete chambering of the cartridge. Excessive headspace permits case stretching and can permit case separation, which will result in high pressure gas leakage during the firing/pressure cycle. Gas leakage can be very dangerous and may cause damage to equipment and injury to the shooter. Headspace is defined and measured differently for each case design. Rimless, rimmed and belted bottleneck cases each have a method unique to the design and a measurement specific to the chambering. Straight walled cases, rimless and rimmed, also have unique methods and cartridge-specific measurements.
Headstamp - Identifying markings/stampings on the base ("head) of a metallic cartridge. The caliber and maker are virtually always identified and there may be additional information such as a date of manufacture.
Heller - A court case (District of Columbia v. Joseph Heller) which was heard by the Supreme Court and resulted in a ruling affirming that the Second Amendment protects an individual's right to possess a firearm independent of membership or service in a militia and that such firearms may be used for self-defense/home defense or other lawful purposes. In particular, the ruling found that Washington, D.C.'s ban on handguns and the restrictions requiring that rifles and shotgun must be kept trigger locked or unloaded and disassembled were unconstitutional.
Hodgdon - A modern gun powder manufacturer
HP - Hollow point (bullet design)
HRC - Rockwell Hardness C Scale. Sometimes written RC.
IMR - Modern gun powder manufacturer: Improved Military Rifle; formerly DuPont
Iron Sights - Any sighting system based on a sight system which does not include sighting optics or gun mounted optical devices.
IWB - Inside the WaistBand. A type of holster which fits inside the waistband of the pants instead of outside the pants. Used for concealment.
Jag - A pointed and ridged, caliber specific, cleaning attachment which typically screws onto a cleaning rod and is used to push patches through the bore.
JHC - Jacketed hollow cavity (bullet design)
JFP - Jacketed flat point (bullet design)
JHP - Jacketed hollow point (bullet design)
JMB or J.M.B. - John Moses Browning. See 'Browning'. A prolific American firearms designer.
KE - Kinetic Energy. See 'Energy'
Keith - Elmer Keith. Keith wrote prolifically for periodicals and also published a number of books on various firearm-related topics, including hunting, revolver shooting and reloading. His reloading efforts with the .44 Special led to the development of the .44Magnum.
KYPD - Keep your powder dry
Land - The raised portion of rifling.
Leade - The portion of the bore forward of the chamber, where the rifling begins.
Locked Breech, Recoil Operated - A semi-automatic/automatic action in which the action is locked closed until recoil has moved the locked barrel/breech sufficiently to initiate an unlocking action which separates the barrel and the breech.
Long Gun - A shoulder-stocked firearm. Not a pistol/handgun.
LOS - Line of sight
LPP - Large pistol primer
LRN - Lead round nose (bullet design)
LRP - Large rifle primer
LSWC - Lead semi-wad cutter (bullet design)
LWC - Lead wad cutter (bullet design)
Mag. - Magazine or magnum.
Magazine - Ammunition holders (either integral to a firearm or detachable) that are typically equipped with a spring to move the stored ammo into position for feeding. Sometimes referred to carelessly or using slang as 'clips'.
MAP - Maximum Average Pressure, a term used by SAAMI to indicate "the recommended maximum pressure level for loading a particular type of commercial ammunition."
McDonald - A court case (McDonald v, City of Chicago) which was heard by the Supreme Court and resulted in a ruling that the Second Amendment's protection of the individual right to own and use firearms for lawful purposes (per the earlier Heller ruling) must be respected by state and local governments, not just by federal law.
MIM - Metal Injection Molding. A process involving the creation of parts in forms from metal powder. It results in tight dimensions on the finished part without the need for final machining and is therefore very attractive to manufacturers. Commonly considered to be a cost-cutting measure by the firearms community and therefore undesirable.
MM - Millimeters; also mm
MV - Muzzle velocity, usually in fps, but also in meters per second in most of Europe. Velocity of the bullet at or very near the muzzle of the barrel
MOA - Minute of angle. Degrees are broken down into minutes and seconds, just as hours are. There are 60 minutes in a degree and 60 seconds in a minute. If the muzzle of the rifle is placed at the center of an imaginary circle with the target on the circumference of the circle, then the distance between impacts on a target can be measured as distances on the circle using angles. 1 Minute of angle at 100 yards is approximately 1.047", usually simplified to 1". Similarly, 1 MOA at 25 yards corresponds to about 0.25" and to about 5" at 500 yards.
Momentum - A scientific quantity that relates to how difficult it is to stop a moving object. The Power Factor calculation used to classify cartridges in some pistol competitions is a scaled version of momentum.
Muzzle - The front portion of the barrel surrounding the hole where the bullet exits. Also to point a gun at someone, generally unintentionally.
NAA - North American Arms, a manufacturer of firearms
NEF - New England Firearms, a manufacturer of firearms
NFA - National Firearms Act (1934). The NFA, among other things implemented the federal requirement for registration of machineguns, silencers, and short barreled long guns.
NRR - Noise Reduction Rating. The amount hearing protection will reduce the noise power reaching the shooter's ears. Expressed in decibels (dB). Larger numbers mean more noise reduction.
O/U - Over/under (shotgun)
OAL - Overall length - usually refers to the length of a complete cartridge (same as COAL or COL)
Ogive - The curved portion of a bullet ahead of the cylindrical portion or shank. The radius of the ogive is usually expressed in multiples or fractions of the caliber. (pronounced oh-jive)
Open Sights - A type of iron sights in which the user aligns a front and rear sight without sighting through an aperture, usually by placing a post front sight in the notch of the rear sight.
OWB - Outside the WaistBand. A type of holster which is designed to be worn outside the waistband of the pants.
PBR - Point blank range, used to refer to either very close range shooting (e.g.He was shot at point blank range) or to shooting within the range at which a rifle's trajectory does not exceed the size of the desired target and therefore there is no need to adjust the point of aim or the sights and the shooter may simply hold on the center of the target. (e.g. With a 120gr bullet, this rifle's point blank range on an 8" target is 305 yards).
PDW - Personal Defense Weapon
PFL - Partial full length die
Pistol - Handgun. In modern times, the term 'pistol' is sometimes used to refer exclusively to handguns which are not revolvers, but this is not a universally accepted convention.
POA - Point of aim.
POI - Point of impact.
Points - Per BATF's interpretation of the GCA of 1968, handguns must score above a certain arbitrary threshold on a points scheme where points are awarded based on a set of rules supposedly designed to prevent the import of low quality and/or non-sporting handguns.
Polygonal Rifling - A rifling system consisting of a bore shaped like a polygon rather than having distinct lands and grooves. Employed by Kahr, Glock and H&K, among others. Commonly either hexagonal rifling (6 sided polygon) or octagonal rifling (8 sided polygon).
PPC - A cartridge designed in 1974 by Dr. Louis Palmisano and Ferris Pindell. Based on the 220 Russian case with a head diameter of .441 - .445. Considered to be the most efficient cartridge design available, the .22 cal PPC and 6mm PPC virtually dominated benchrest accuracy competition for many years.
Primer - A small explosive charge that fires upon impact from the firing pin and provides the energy/heat to ignite the powder charge. A primer may be self-contained in a metal cap that fits into the center of the base ("head") of a centerfire cartridge or may be contained in the hollow rim of a rimfire cartridge base.
PSI - Pounds per square inch; also: psi. This is the normally accepted measure of pressure exerted on the inside wall of the chamber of a modern rifle or handgun during the firing cycle. In times past, pressure was measured in CUP but PSI is a more accurate pressure measurement and requires less complicated measuring equipment. PSI is replacing the use of CUP as a standard reference of pressure in all firearms testing and pressure proofing.
RC - Rockwell Hardness C Scale. Sometimes written HRC.
Revolver - A type of handgun/pistol with a revolving cylinder containing multiple chambers. The chambers can be fired, in turn, by either pulling the trigger (double action) or by cocking the hammer and pulling the trigger (single action). There have also been a very few "automatic revolvers" where the recoil of the gun advanced the cylinder.
Repeater - Any firearm which can fire more than one shot without being reloaded. i.e. Not a single shot firearm.
Rifle - A long gun with a rifled bore, designed to be fired from the shoulder.
Rimfire - A cartridge with the primer contained in the hollow rim of the base ("head") of the cartridge. Also a firearm chambered for a rimfire caliber.
RN - Round nose (bullet design)
S&W - Smith & Wesson
SA - Single action, as opposed to double action (DA), SA releases the hammer/striker for primer contact and firing AFTER cocking of the hammer/striker and positioning of the cartridge for firing is accomplished by means other than pulling the trigger. Also less commonly, Semi-Automatic.
SAA - Single Action Army; a famous design of revolver by Colt used in early America and credited with finalizing the popularity of mass produced, brass cartridge handguns. This is the cowboy revolver of Hollywood Western Motion Pictures.
SAAMI - Sporting Arms and Ammunition Manufacturers Institute; an accredited standards developer for the American National Standards Institute (ANSI)
SAF - Second Amendment Foundation
SAO - Single action only
SB - Small base die
SBR - Short Barrel Rifle. The NFA of 1934 places a minimum length on the barrel of a gun with a rifled barrel and a shoulder stock. Any shoulder stocked firearm with a rifled barrel which does not meet the barrel length limit is an SBR and must be registered per NRA restrictions.
SBS - Short Barrel Shotgun. The NFA of 1934 places a minimum barrel length on a gun with a smoothbore and a shoulder stock. Any shoulder stocked firearm with a smooth bore which does not meet the barrel length limit is an SBS and must be registered per NRA restrictions.
SD - Self Defense. Also sectional density; ratio of bullet's weight, in pounds, to its cross-sectional area, in inches.
Select Fire - Also Selective Fire. A firearm which can operate either as a semi-automatic or as a fully automatic/burst fire weapon depending on the setting of a selector switch.
Semi-automatic - A firearm which performs the actions of firing, extraction/ejection of the empty case, loading of a new round from the magazine and, if necessary, cocking, each time the trigger is pulled. A semi-automatic firearm will fire one shot per trigger pull until the magazine is empty. Also referred to as 'autoloading', 'self-loading' or, less accurately, as 'automatic'.
Shotgun - A long gun with a smooth bore, designed to be fired from the shoulder.
SJHP - Semi-jacketed hollow point
SKS - Samozaryadnaya Karabina Simonova, or Self-loading carbine Simonov. Sergei Gavrilovich Simonov was one of the old Soviet Union's foremost arms designers. The rifle was adopted by the USSR in 1945, and was made both there and in China.
SLR - Self loading rifle
Slug - Most commonly used to refer to a solid projectile close to bore diameter (vs. one of many pellets much smaller than bore diameter) that is fired out of a shotgun. Also sometimes used as a synonym for 'bullet'. Also, the unit of mass in the United States Customary measurement system.
SMG - Sub-machine gun. A compact full-auto weapon typically chambered for a pistol cartridge.
SP - Soft point (a bullet design)
SPP - Small pistol primer
SRP - Small rifle primer
Standard Conditions - Ballistic Coefficient values are based on standard conditions of 59 degrees Fahrenheit and 29.53mm of mercury. For precise results, BC figures should be adjusted based on actual temperature and pressure measurements taken at the time of firing.
Sturm Ruger - Ruger Firearms. Alexander Sturm was a co-founder of Ruger and a good friend of William Batterman Ruger. He provided startup capital and also designed the Ruger eagle trademark. When Sturm died at the age of 28, Ruger changed the color of the Ruger eagle trademark from red to black.
Striker - A "spring-powered" firing pin. Rather than being struck by a hammer, a striker is released by the trigger/sear and driven forward by spring pressure to hit the primer.
SWC - Semi wadcutter (a bullet design), semi-wadcutters typically have a truncated cone nose but a sharp shoulder of full diameter. These bullets cut full diameter holes in targets but are more aerodynamic than full wadcutters and are more of a general purpose bullet than a full wadcutter
TC - Truncated cone (a bullet design)
Throat - Leade, freebore. The portion of the barrel immediately forward of the chamber. In some rifle chamber designs, the throat may be long and may transition into a relatively slow taper to full depth of lands and grooves (rifling). In other rifle designs the throat is relatively short and the transition to full depth rifling is abrupt, although all barrels have some taper from throat to full depth rifling. The immediate effect of the two extremes in design is to determine the maximum distance a bullet may protrude out the front of the case. This determines the final overall length of the loaded cartridge, for a given bullet shape.
Timing - A term that describes the proper function of a revolver. A number of processes must take place in the proper order during process of advancing the cylinder, locking it in place and cocking the hammer. If those process are not taking place as they should the revolver may be said to have "gone out of time".
TMJ - Total metal jacket (a bullet design) similar to full metal jacket, but with the base of the bullet also enclosed by the jacket.
Trajectory - The path traveled by the projectile as it moves from the muzzle of the firearm to the target. The trajectory is determined primarily by the angle of the bore, the initial projectile velocity, gravity, by wind and by air resistance although there are other less significant factors involved.
WBY - Weatherby
WC - Wad cutter (a bullet design), wad cutters have flat noses and sharp shoulders. Wadcutters cut neat, full diameter holes in targets which facilitates scoring.
Windage - Horizontal deflection on the target or of the sights.
Wind Value - A simple scaling factor used to determine the effect of wind on bullet deflection. If the wind is at more or less right angles to the direction of bullet travel, it is considered to be a full value wind. At about 30 degrees of angle to the direction of bullet travel it would be called a half value wind.
WWB - Winchester White Box. Winchester USA marked ammunition. Common budget practice ammunition, often bulk packed and available in common rifle and pistol calibers.
USRAC - U.S. Repeating Arms Company; firearms, ammo and reloading component manufacturer
Zero - The sight setting which puts a bullet at the point of aim at a given distance. e.g. The rifle has a 100 yard zero. Also the process of adjusting the sights to achieve a point of aim/point of impact correspondence at a desired distance. e.g. I need to zero my rifle.