This is a continuation of the KNOW THY TERMS Series.

We split this series into two categories:

-        Part I: Legal Industry Terms

-        Part II: Firearm Industry Terms

Know Thy Terms Pt2

This educational series is not a comprehensive list, but we feel like we covered a good amount of the firearm industry terms. That being said, if you think of something we should add, let us know by commenting below!

Term Short Description Long Description
(F)DE (Flat) Dark Earth A specific type of coloring. Flat is the finished look, Dark Earth is the color.
2A Second Amendment The reason that we have all of these awesome acronyms.
A-2 Birdcage A specific type of flash hider where the prongs are enclosed. Most often recognized as the muzzle device of choice by our Armed Forces on the M16 and M4 platforms.
Ablative A sacrificial substance used to absorb or disperse heat by burning off, thereby reducing the sound. When you hear someone talk about shooting a suppressor “wet,” the substance they use in the silencer (water, wire pulling gel, suppressor foam) is referred to as the ablative.
AL Aluminum An inexpensive, flexible, lightweight metal more commonly used for the construction of rimfire and pistol silencers. 
AOW Any Other Weapon A type of firearm that is not defined by the major ATF categories, such as SBR, SBS, Silencer, Pistol, Rifle, or Shotgun. Firearms not under the designation of these categories still need to be registered as an AOW. 
ASR Active Spring Retention A SilencerCo mounting system that was originally used on the SWR Specwar.  It has since been incorporated into all of the SilencerCo rifle silencers. 
Baffle Geometry The way the baffles are shaped directly affects how the gases flow through the silencer, resulting in changes of blowback and sound.
BBL Barrel The long skinny part that the bullet goes through :)
BCG Bolt Carrier Group BCG's are referenced a lot because they are basically the heart of AR's and M-16's. 

A term to describe gases moving in opposition to the direction of the projectile. For instance, when you shoot and the gases go forward, but some of the gases blow backward due to added resistance of a silencer at the muzzle of a firearm.

Can Aka suppressor, aka silencer. It has many names but refers to the same awesome thing.
Carbon Fouling The residue from the combustion of gunpowder. To some degree, a thin layer of residue can help with attenuation in rifles, but in the case of pistol and rimfire, the suppressor needs to be cleaned in order to prevent too much build up. 
Click Together A particular method of baffle assembly where the silencer baffles click onto one another in order to seal the hot gases inside of the baffles, thereby preventing fouling on the inside of the tube. 
CQB Close Quarters Battle A fighting style used by the military. In silencers, this term is often used to denote a shorter or more maneuverable silencer.
dB Decibel A measurement of sound. 
DDs Destructive Devices The term used for explosive devices such as commercial explosives, flash bangs, grenades, etc..
DI Direct Impingement This is a reference to a gas system common to AR's.
DT Direct-Thread The simplest type of mounting system where the suppressor directly threads onto the host firearm.
Endcap The endcap is screwed on to the end of the silencer. Generally used for modular silencers when changing lengths. You can also change an endcap out to change the bore size to match the caliber of the host firearm.
FH We've covered a lot on muzzle devices before. But a flash hider is a device used to do just that - reduce the muzzle flash while shooting. See also, muzzle brake.
FPS Feet Per Second Generally used in the silencer world in the context of determining whether or not a round is considered subsonic. FPS can generally be found on the ammo box. 
FRP First Round Pop FRP is the louder sound made from the initial blast of the firearm due to the amount of oxygen in the suppressor. Subsequent rounds fired after the first round will be a little bit quieter. 
FS Flash Signature The flash emitted from the barrel of a firearm when a round is shot through it. 
Gr Grain A reference to grain weight of projectiles and/or powder.
HD Home Defense
Hydro Sonic Waterbased cleaning system that vibrates the water molecules to clean metal materials.
ID Inner Diameter Commonly used to describe the inside diameter of a silencer tube.
K Kurtz An abbreviation for the German word: "Kurtz." Meaning "Short."
K-Baffle One of the major styles of baffles where the profile view of the baffle resembles the letter “k.”
LH Left-hand Direction threads are done on a barrel or muzzle device. It is a common reference when describing thread pitch.
Lower In reference to a section of an AR that houses the fire control components. By law, the lower of a firearm is the section that holds the serial number.
M Modular This letter is used after model names to represent that the can is modular.
MB Muzzle Brake We've covered a lot on muzzle devices before. A muzzle brake is intended to reduce lateral recoil of a firearm by specifically controlling escaping muzzle gasses. See also, flash hider.
MOA Minute of Angle A method of measuring angle in relation to distance.  This is most often used to describe the precision of a firearm where a one inch group at 100 yards represents 1 MOA, 2 inches at 100 yards indicates 2 MOA, etc. 
Monocore Used when describing the inner part (baffles) of a suppressor being machined out of one solid piece.
Muzzle Device This term is used to reference a device that screws onto the end of a firearm. Examples of muzzle devices are flash hiders and muzzle brakes.
Nielsen Also known as a booster, the nielsen device is used for pistol suppressors in order to compensate for the recoil of the host firearm. Another common technical term is “linear decoupling device.”
OAL Overall Length Applies to length of silencer or how the ATF defines specific firearms in order to determine what category they are in. The OAL is a requirement on every NFA form (excepting oddballs like auto sears).
OD(G) Olive Drab (Green) or Outer Diameter A specific type of green coloring. Depending on context, OD is also referred to as the Outer Diameter in reference to a silencer or barrel. 
PCC Pistol Caliber Carbine A rifle that fires traditional pistol calibers.
PDW Personal Defense Weapon Though not legally defined, PDW’s are often a very small, subcompact firearms.
Piston The part of the nielsen device that threads onto the barrel that allows the weight of the silencer to disconnect from the tilting barrel of a Browning action pistol. 
POA Point of Aim Where you are aiming (or where it looks like the bullet will hit).
POI Point of Impact Where you actually hit (or where the bullet makes the impact).
PSI Pounds Per Square Inch A measure of pressure most commonly referred to when talking about catridge specifications.
QD Quick-Disconnect Also known as QA (or Quick Attach). A type of mount that allows you to quickly mount or remove a silencer. Generally a female mount on the silencer that accepts a male muzzle device. 
RH Right Hand Directions threads are done on a barrel. It is a common reference when describing thread pitch.
Rnd Round
ROF Rate of Fire The rate at which a firearm can launch a projectiles. Typically described as round count/time.
SBR Short-Barreled Rifle A rifle with a barrel length less than 16 inches. SBR's are registered through a specific NFA form. 
SBS Short-Barreled Shotgun A shotgun with a barrel length of less than 18 inches. SBS's are registered through a specific NFA form. 
SD Shalldampfer German for: sound damper. The suppressed version of a firearm. For example, the MP5 vs. the MP5-SD.
Serials Serial Numbers The social security number of firearms and some firearm accessories. 
Shim A circular "washer like device" that is used to time a muzzle device correctly onto a host firearm. 
Shoulder A particular section of a barrel, at the base of the threads, but before the start of the barrel, that allows the object being threaded on to the barrel to have a perfectly flush mount onto the host firearm. The two forms of shoulders are taper and square. 
SS Stainless Steel A tough, flexible metal resistant to corrosion. These steels can generally be used for the construction any silencer where a primary goal is durability as opposed to weight savings. Stainless steel, especially in rimfire cans, give you more options for cleaning as well. 
Subs Subsonic Ammo The premise of a subsonic bullet is to have the projectile exit the barrel at a velocity that is slower than the speed of sound.
Supers Supersonic Ammo A reference to ammunitions where the projectile will always be faster than the speed of sound. 
SURG Suppressed Upper Receiver Group Adopted into the civilian market from a military acronym, SURG refers to an AR upper receiver that has in integrated silencer.
Taper In regard to the barrel or muzzle devices shoulder, a taper replaces the 90 degree shoulder on a barrel or device to create a more reliable/repeatable mating between silencer, muzzle device and/or barrel. 
The Dip A way of cleaning metal materials by dipping them into a chemical mixture.  This is not a practice that we advocate due to the unnecessary hazard of the chemicals… though we know the curious among you can find details elsewhere.
Threaded Barrel A barrel that is threaded is used primarily to mount a silencer onto a host firearm (the alternative use is for an AR platform where a muzzle device would be mounted on).
Ti Titanium A metal with a high strength to weight ratio though more expensive than most stainless steels or aluminum. 
TM Taper Mount The most repeatable and accurate POI as far as QD goes. See also: Taper
TPI Threads Per Inch A measurement for the threading on a barrel. 
Tube The outer most part of a silencer, generally covering the baffles.
Upper In reference to a section of the top section of an AR containing the upper receiver, barrel, handguard, etc.. 
Wet Tumbling A cleaning system that tumbles in order to clean metal materials.
H1 Thru H-9 Buffer Weights By changing the buffer weight, you can slow down or speed up the cycle of the gun. Altering the buffer weight helps compensate for the pressure added or taken away from the firearm. 
OTB Over The Barrel Type of silencer where the silencer mounts over the barrel of the firearm.  This, in turn, reduces the OAL of the suppressed system at the cost of sound attenuation. AKA: Reflex
FA (rated) Full Auto Rated In terms of suppressors, a can that is considered full auto rated is one that is built from specific materials in order to withstand the heat and pressure associated with a high rate of fire.