Firearms Terminology: Guns for Beginners

Reader Anner writes:

True Believers get all wrapped up in proper firearms terminology. Avoid that next lecture from the old coot behind the counter by studying this partial guide to proper firearms terminology:

Caliber – The diameter of the firearm’s bore, expressed as a fraction of an inch. “.30 caliber” is 3/10 of an inch wide.  Depending on manufacturer’s specifications, this may denote the diameter of the bullet, cartridge mouth, barrel lands, or barrel grooves. Europeans generally measure barrel lands, while American manufacturers use barrel grooves (which is usually the actual bullet diameter).  When ammo manufacturers create a new cartridge, they need it to sell. They will often choose a name that does not accurately describe its actual size. For example, .223 Remington is actually a .224” bullet; .300Blackout is actually a .308” bullet. Reference a reloading manual or the manufacturer’s website for accurate specifications . . .

XXmm – A metric version of denoting bullet diameter. 9mm is the diameter of the bullet, barrel, or related object. Again, Europeans differ in what they actually measure.

Caliber vs. XXmm vs. What ammo do I buy? – When in doubt, look at what’s imprinted on the barrel and purchase ammunition identical in nomenclature. Be wary of +P, Magnum, or Short Magnum designations (see below).

Cartridge – The entire components of a loaded case, primer, powder, and bullet.

Bullet – The projectile that exits the barrel under pressure from the burning powder and expanding gases.

Shell – Also called the ‘case’; the container that houses the other components of a cartridge. Among shotguns, ‘shell’ is analogous to ‘cartridge’.

Primer – The small, circular component at the rear of a cartridge struck by a firing pin, which detonates the powder.

Brass – The empty case or shell.  Common use is to refer to the reloading component as “brass”, or a fired round as “spent brass.”

Magazine – The device that stores cartridges until the firearm’s action positions them into the chamber for firing.  Most repeater firearms except revolving handguns use a magazine. Bolt-action rifles that hold extra cartridges internally still technically use a magazine, though it is not detachable. Lever action rifles with an ammunition tube below the barrel also use a magazine; it is a tube magazine.

Clip – This is different than a magazine. A clip is a small metal piece that secures loose ammunition for loading into a magazine. One example is the M1 Garand en-bloc clip, which holds eight rounds of .30-06 ammunition for loading into the Garand’s internal magazine. The M-16 family of rifles is capable of using 10-round stripper clips to feed the larger 20-round or 30-round magazines, though this practice is not common. Very few firearms use a clip.

Single Action (SA) – The hammer is pre-cocked and ready to fire upon lightly pressing the trigger. Handgun examples include the Browning Hi-Power, 1911, and Colt Single Action Army. The vast majority of rifles and shotguns are single action, including bolt-action and lever-action rifles. Single action firearms generally have a light trigger pull and short trigger travel, necessitating extra caution.  Many SA firearms incorporate additional safeties, all secondary to proper gun handling.

Double Action (DA) – Pulling the trigger both cocks the hammer and releases it to fire.  Examples include Smith & Wesson revolvers (though, if you cock the hammer manually it turns into a single action).  DA triggers are generally heavier and require longer trigger travel to fire as compared to SA firearms.

DA/SA – Any firearm that offers you the option of both DA and SA fire.  Two common examples:  A S&W revolver has an exposed hammer, which allows you to cock the hammer then pull the trigger (SA), or to simply pull the trigger and let the trigger pull back the hammer before firing (DA).  Also, most Sig-Sauer and HK pistols are DA on the first shot but revert to SA fire once the slide has cycled.

Decocker – Most DA/SA pistols also incorporate a lever that safely lowers the hammer from SA mode to DA mode.  HK builds this into the safety lever, while Sig-Sauer has a separate decocking lever.  This can be useful after a stressful situation, in which you’ve fired and wish to return to the heavier trigger pull of DA mode to prevent a negligent discharge.  As always, proper firearms safety is more important than a mechanical device.

Striker-Fired – Just to confuse the matter, some pistols do not use a hammer at all.  Instead, they use a ‘striker’ that acts as the hammer.  The striker is captured by a spring, partially cocked when the slide cycles, and fully cocked and released when the trigger is pulled.  For the purposes of handling, treat these as SA.  However, the trigger often feels midway between a DA and SA.  Examples include Glock pistols, Springfield XD series, and S&W M&P series.

Handgun – Any firearm fired using your hands only, without a stock for securing against your shoulder.  Some handguns can be very large, requiring both hands to hold.

Pistol – A semi-automatic handgun.  Pistol is commonly misused to reference all handguns, including revolvers.

Revolver – A handgun with a rotating cylinder that holds the cartridges.

Derringer – A small double-barreled handgun.  Offered by various companies from .22LR to .410 shotgun, derringers are limited in value due to a low capacity and terrible ergonomics.  They can be dangerous if mishandled, due to a heavy hammer cocking motion, single-action trigger, and short barrel.

Sidearm – A police/military term for a supplementary weapon.  It usually denotes a handgun, but can be a shotgun, secondary rifle, etc.  Sidearm is not in common use outside of police or military units.

AR = Armalite – Eugene Stoner designed the rifle that led to today’s wide range of M16-inspired designs.  Mr. Stoner worked for Armalite, an aerospace manufacturing company.  The Armalite firearms company still exists today, producing high quality rifles.  AR was originally a reference to the Armalite name, but has been hijacked as ‘assault rifle’, a fictitious reference to the various forms of the parent AR-15 rifle.

MSR = Modern Sporting Rifle – In response to the creation of the terms “assault rifle” and “assault weapons”, in which a name and cosmetic features played a role in legislation passed by congress (most notably the Assault Weapons Ban of 1994), gun rights supporters pushed back.  Given that the AR platform is ideal for various sporting uses, such as varmint and hog hunting, the term MSR emerged to reflect the AR’s common use as a hunting platform.  Keep in mind, the 2A has nothing whatsoever to do with hunting or tradition—it is squarely aimed at preventing government tyranny—but in supporting 2A, words matter.  An uninformed voting public will latch onto words, and scary words drive votes.

SS = subsonic – Most modern cartridges fire a bullet at supersonic speeds, creating a ‘crack’ as the bullet leaves a mini-sonic boom in its wake.  Subsonic loads are much quieter out of a rifle, and slightly quieter out of a handgun.  Except for +P loads, standard 45ACP loads are generally subsonic out of a handgun.

LRN = Lead round nose – LRN bullets are ideal for shooting steel targets, as the soft lead splatters on the target.  FMJ rounds tend to deform the steel, or invert ricochet at the shooter.  This situation has killed people, so be careful of your target and your ammo.

FMJ = Full metal jacket – The core of a bullet is usually lead.  On FMJ rounds, this core is surrounded by a metal jacket, usually copper or tin alloys.  The jacket may only cover the forward section of the bullet, leaving the base as exposed lead.  FMJ rounds are cleaner to shoot than solid lead rounds, with less chance of fouling in the barrel and action, and less lead exposed to the environment.

TMJ = Total metal jacket – The entire bullet is encased in a jacket material.  For indoor shooting ranges, TMJ offers the lowest chance of lead particles fouling the air.

Plated – Similar to TMJ, plated bullets are lead cores with a thin coat of metal on all sides.  Instead of a thick metal jacket, the plating is thin but effective.  Plating is just as clean as TMJ when cycling and firing, but much cheaper to produce.

HP = hollow-point – HPs are designed to expand on impact for more tissue/target damage and less chance of over-penetrating and striking something on the other side of the target.  HPs are suitable for hunting and self-defense.

+P – Standard pressure rounds are listed under SAAMI specifications for maximum chamber pressure, expressed in PSI.  Loads that exceed these standard pressures are denoted +P.  Some loads are rated higher at +P+, though this designation is not recognized by SAAMI and carries no manufacturer guarantee of safe function.  Not all firearms are designed to handle +P loads; the instruction manual and barrel of the firearm should clearly communicate this information.  +P loads can provide a meaningful increase in muzzle velocity, potentially translating to better terminal performance.  However, there is a compromise:  +P loads also produce more muzzle blast, recoil, and wear on the firearm.  If you intend to carry +P loads, test them thoroughly in your firearm for reliability and accuracy.  In semi-automatic firearms, you may consider heavier recoil springs to counter the increased slide cycling speed.

Magnum – In French champagne country, a magnum is a unit of measurement.  It is larger than a standard size champagne bottle.  American firearms manufacturers adopted the term as they experimented with modern smokeless powders, most notably in the 1930’s while developing the .357Magnum.  The large increase in chamber pressure necessitated a distinction for rounds developed with modern powders.

This can get confusing.  Standard pressure for a .357 Magnum is vastly different from standard pressure for a .38Special (the parent cartridge from which the .357 Magnum was developed).  Magnum doesn’t just denote a change in pressure, such as the designation +P.  It denotes an entirely different cartridge.  .357 Magnum cases are slightly longer than .38Special cases.  The size difference doesn’t mean much; it was a safety feature to avoid loading a .357 Magnum cartridge into a firearm designed for .38Special.  However, the .357 Magnum is developed with more powder as its standard load.  You could load a .38Special to the same pressure as .357 Magnum (there’s plenty of room for that much powder).  However, doing so will split the case (case walls are thinner) and likely harm the shooter or firearm.

To further confuse the matter, some older cartridges are offered in +P.  In a .357 Mag revolver, you can fire .38Special, .38 Special+P, or .357 Magnum (as well as some ancient cartridges, such as .38S&W Long).  However, a .38Special revolver will denote if it’s rated for +P.  If not, stick to standard pressure loads.  If it is +P, you can fire .38 Special or .38 Special +P, but not .357 Magnum.

Bottom-line:  Purchase ammunition identical to the marking on the barrel, or thoroughly research other safe options before pulling the trigger.

Short Magnum – In the late 1990’s, Winchester experimented with taking large cartridges, such as .300WinMag, and generating the same ballistics out of a shorter, fatter case.  Such cartridges, such as the .300 Winchester Short Magnum (.300WSM), provide shorter and lighter actions to cycle the round, decreasing the overall weight and length of the rifle.  However, WSM and WSSM (Winchester Super Short Magnum) cartridges are not interchangeable with their parent cartridges.

FTF – Failure to feed – A malfunction that occurs when a firearm jams as it attempts to insert a new cartridge into the chamber.  Most FTF problems are due to cheap or broken magazines.  Quality magazines from reputable manufacturers fix this issue.  If the magazine is not at fault, a dirty/unpolished feed ramp, poor quality ammunition, or more complex issues may exist.

FTE – Failure to extract – Similar to FTF, but the failure occurs as the fired shell does not properly extract/eject.  This is usually related to the extractor and ejector assemblies, either of which may require a spring change or polishing.  In both FTF and FTE situations, online videos and forums provide excellent support from others who have had similar experiences.

Barrel porting – Holes drilled directly into the barrel between the 11 and 1 o’clock positions.  The holes direct expanding gases upward, reducing muzzle flip and/or perceived recoil.

Muzzle brake – A muzzle device, usually detachable, with holes, vents, fins, etc. that direct gasses rearward to primarily reduce recoil.  Muzzle brakes send a sharp shockwave of gas to the shooter’s rear quarters, impacting those standing nearby.  Muzzle brakes may also feature vertical holes to reduce muzzle flip, confusing the distinction with compensators.

Compensator – A muzzle device, possibly detachable, that directs gasses upwards to reduce muzzle flip.  A compensator may borrow some muzzle brake features and reduce recoil.  The line between muzzle brakes and compensators can be blurry at times.

Flash hider – A muzzle device, usually detachable, that dissipates unburned powder as it exits the muzzle.  Unburned powder commonly burns just as it leaves the barrel, producing a fireball or flash.  Flash hiders send this powder in specific directions, to mitigate the visual signature of a gunshot.  Flash hiders can be useful when hunting near dark, to avoid blinding the shooter.

BUIS = backup iron sights – Many modern rifles and some shotguns now only arrive with a picatinny rail and no open sights.  A common AR term is COR, or carbine/optics ready.  For a hunting rifle, a scope is adequate.  For a defensive rifle, where a dead battery on a red-dot optic can render the firearm nearly useless or dangerous, BUIS are essential.  Metal BUIS are expensive and heavy.  I recommend the MagPul polymer BUIS.  They’re cheaper, lighter, and tough.  I’ve used them on ARs and shotguns to great effect.

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