Pistol Grips& Gun Accessories

For acronyms and abbreviations in general, see this or this.

Here is the list of acronyms and abbreviations specific to AR-15 and AR15:

@ - When prefixed to a member's name, means that the following comment is directed "at" or to that member.
. - Used to add a post without typing anything, means "+1 to my post count, I have no new comment" or the same thing as BTT. Also sometimes left behind as a placeholder when someone deletes the content from a post or as a quick post to tag a thread.
+1 - When used with a quote, means the same thing as "Ditto" or "I agree". When used in the EE feedback forum, means a good experience with either a buyer or seller. When just posted with no reference, it means "+1 to my post count, I have no new comment" or the same thing as BTT...
-1 - When used in the EE feedback forum, means a bad experience with either a buyer or seller.
87 - A nonsensical answer to nonsensical numerical questions. For example, someone might ask "How many magazines should I buy?" There is no meaningful answer to this question because it varies according to each persons' unique circumstances, so the canned answer becomes "87". Originated by markm, presumably because he felt it a waste of time to answer such questions, it has since taken on a life of its own and is used by others who think it makes a funny in-joke. The number 87 is also associated with several other meanings in general usage.
88 - Short hand for a neo-Nazi or, more loosely, any white supremacist. Derived from "H" being the 8'th letter in the alphabet, and HH being an abbreviation for "Heil Hitler". The number 88 is also associated with several other meanings in general usage.

mspmwg3

AR-15 Acronyms A

A1 - Of or referring to a characteristic of the M16A1 (for example, an A1 rear sight)
A2 - Of or referring to a characteristic of the M16A2 (for example, an A2 flash hider)
A3 - Of or referring to a characteristic of the M16A3, or (in civilian parlance) a flat-top receiver. Note that the M16A3 is essentially just a full-auto M16A2, but civilian manufacturers began using the term A3 for flat-top receivers before the military adopted the M16A3 and M16A4, so there is divergence between military and civilian usage of the term "A3". Without a definitive military context, it is most likely that "A3" refers to a flat-top, civilian upper receiver. Note also that some civilian manufacturers call their flat-tops A3, others A4.
A4 - Of or referring to a characteristic of the M16A4 (for example, a flat-top A4 upper receiver)
ABC - Armalite, Bushmaster and Colt (considered by many to be the top three manufacturers of AR-15)
ABCR - Armalite, Bushmaster, Colt and Rock River Arms (a variant of ABC used by those who also consider Rock River Arms to be a top-tier manufacturer)
ACOG - Advanced Combat Optical Gunsight (see Trijicon's website)
ACR - Advanced Combat Rifle (a late 1980's weapon development program intended to replace the M16 - more detail here)
AD - Accidental Discharge (a non-negligent unintentional discharge of a weapon that could not have been reasonably forseen and prevented - e.g. a caused by an unexpected mechanical failure)
ADCO - Not an acronym, just a name (retailer of AR-15s and accessories, provider of AR15 gunsmithing services - website)
AF - Air Force
AFAIK - As Far As I Know
AGNTSA - Aww Geez Not This Stuff Again (substitute more colorful noun for "Stuff" as desired)
AJNTSA - Aww Jeez Not This Stuff Again (substitute more colorful noun for "Stuff" as desired)
AOW - Any Other Weapon (any weapon capable of discharging a shot that is not otherwise categorized under the NFA)
AR - ArmaLite (see explanation here)
ARD - Anti-Reflection Device (a device placed on the objective of an optic to reduce reflections and glare)
ARF - AR15.COM (this site)
ARFCOM - AR15.COM (this site)
ARFCOMMER - One who is a member of this site
A.R.M.S. - Atlantic Research Marketing Systems (manufacturer of rail mounts, systems and accessories - website)
ASA - American Spirit Arms (manufacturer of AR-15 rifles, rifle kits, parts and accessories - website)
ASAR - Abrams Small Arms Research (website)
ATN - American Technologies Network (manufacturer and distributer of weapon optics and night vision equipment - website)
AWB - Assault Weapons Ban
AWOB - Another Waste Of Bandwidth (derogatory comment made by someone who wishes to point out what they consider to be a pointless thread/Ghillie suits.)

mspmwg4

AR-15 Acronyms B

BAC - Bindon Aiming Concept (the idea behind Trijicon optics like the ACOG that are designed to combine the rapid acquisition of unmagnified sights with the accuracy of traditional magnified scopes. Requires the use of both eyes in the manner of OEGs. AR-15)
BAR - Beyond All Repair
BAR - Browning Automatic Rifle
BBL - Barrel
BC - Ballistic Coefficient (a measure of a bullet's ability to slip through the air unhindered by drag - higher values indicate more streamlined bullets)
B/C/CH - Bolt, Carrier, Charging Handle (the assembly of parts that cycles rounds into the chamber)
BCG - Bolt Carrier Group (the bolt, bolt carrier, gas key, cam pin, etc.)
BDC - Bullet Drop Compensator (a mechanism in a sight to compensate for a bullet's trajectory drop at long distances)
BDU - Battle Dress Uniform
BFA - Blank Firing Adapter
BFD - Big Freakin' Deal (substitute for "Freakin'" as desired)
BFI - Bushmaster Firearms, Inc. (manufacturer of many AR-style rifles - Ghillie suits)
BG - Bad Guy (the only kind of person who should ever be at the other end of your AR15)
BG - Battlegrip (enhanced handgrip made by TangoDown - website)
BH - Black Hills (manufacturer of a variety of new, remanufactured and special purpose ammunition - website)
BHO - Bolt Hold Open (a mechanism that holds the bolt open when the magazine is empty, allowing for faster reloads pistol grips)
BIY - Build It Yourself
BL - Bayonet Lug
BM - Bushmaster (manufacturer of many AR-style rifles - website)
BOB - Bug Out Bag (a bag filled with the necessities you will need to survive in the event you are forced to flee your home on a moment's notice)
BOHICA - Bend Over Here It Comes Again
BOTD - Babe Of The Day (something now reserved for the Team Forum only) posted as warning for any thread containing an image unsuitable for viewing at work)
BRASS - Breathe-Relax-Aim-Slack-Squeeze (mnemonic for steps of accurate shooting - there are many variants of this including Breath-Relax-Aim-Sight-Squeeze and Breath-Relax-Aim-Squeeze)
BRASSF - Breathe-Relax-Aim-Stop-Squeeze-Follow Through (mnemonic for steps of accurate shooting as taught by the USMC - more detail here)
BRD - Black Rifle Disease (a mysterious ailment in which the sufferer develops an insatiable desire for more and more AR-15s)
BSZ - Battle Sight Zero
BT - Boat Tail (a bullet that tapers at the back like the tail of a boat rather than cuts off at a right angle - see the Ammo Oracle)
BTT - Back To Top (adding a post to a thread to bring the thread back to the top of the list of active threads)
BTW - By The Way
BUIS - Backup Iron Sight
BZO - Battle Sight Zero

mspmwg5

AR-15 Acronym C

C3 - Class 3 (a class of restricted weapons as defined by the NFA, including machineguns, supressors, short-barrelled rifles, short-barrelled shotguns, etc.)
CAA - Command Arms Gun Accessories (manufacturer of accessories and gear for various weapons - AR15)
CAR - Carbine
C.A.R. - Colt Automatic Rifle
CC - Concealed Carry
CCH - Cut Carry Handle (a carry handle cut down to form a BUIS)
CCL - Concealed Carry License
CCO - Close Combat Optic (an optic designed for close range use, typically low power, parallax free and with long eye relief. The Aimpoint M68 is an example.)
CCP - Concealed Carry Permit
CCW - Concealed Carry Weapon
CH - Carry Handle
CH - Charging Handle
CIII - Class 3 (a class of restricted weapons as defined by the NFA, including machineguns, supressors, short-barrelled rifles, short-barrelled shotguns, etc.)
CLE - Compass Lake Engineering (manufacturer of competition service rifles and space guns - website)
CLIN - Contract Line Item Number
CLP - Cleaner, Lubricant, Protectant (all-purpose gun maintenance product - example one, example two, Fiber optic sight three)
CMP - Civilian Marksmanship Program (website)
CMMG - Not an acronym, just a name (retailer of AR-15, parts and accessories - website)
CMT - Continental Machine and Tool (contract manufacturer of AR15 uppers and lowers)
COC - Code Of Conduct (the rules governing your use of this site)
COLL - Collapsible (as in a collapsible stock)
CONUS - Continental United States (the lower 48 states and the District of Columbia, not including Alaska or Hawaii)
CQB - Close Quarters Battle
CQ/T (also CQT) - Close Quarters / Tactical (a 1-3x optic made by Leupold and designed for close quarters battle with some mid-range capability as well)
C&R - Curios and Relics (firearms that are officially recognized as collectible due to some unique quality such as age. The ATF maintains a list of qualified C&R firearms that C&R license holders can purchase via interstate commerce without the services of an FFL dealer. More information)
CTR - Compact/Type Restricted (an adjustable carbine stock made by Magpul, with a friction lock feature)
CYA - Cover Your Ass

mspmwg6

AR-15 Acronyms D

DC - Dust Cover
DCH - Detachable Carry Handle
DCM - Director of Civilian Marksmanship (replaced by the CMP)
DD - Daniel Defense (manufacturer of free floating railed handguards, slings and accessories - website)
DD - Destructive Device (an explosive, incendiary, or poison gas device as defined by the NFA)
DEWAT - De-activated War Trophy (a machine gun whose barrel has been plugged and welded to the receiver and whose chamber has been welded shut, rendering it unserviceable but still subject to the regulations of the NFA)
DIAS - Drop-In Auto Sear (a device used to convert a semi-automatic gun to full-auto. By itself considered to be a machine gun under the NFA, and unregistered ones are illegal to even possess with, let alone install in, the guns they convert)
DILLIGAF - Do I Look Like I Give A pistol grip
DIY - Do It Yourself
DOD - Department Of Defense
DPMS - Defense Procurement Manufacturing Services (builder of AR-15 rifles and supplier of parts and accessories - website)
DRMO - Defense Reutilization Marketing Office (an office of the DRMS - website)
DRMS - Defense Reutilization Marketing Service (a government agency that disposes of excess property received from the military services - website)
DSA - D.S. Arms (specializes in FAL rifles, but also sells AR-15 parts and AR-15 accessories - website)
DU - Democratic Underground (a site for the exchange of what are considered liberal ideas - not friendly to your Second Amendment rights)

EA - Essential Arms (manufacturer of AR-15 lowers, stocks and parts - website)
EBR - Evil Black Rifle (a twist on the gun-grabbers' propaganda, embraced by supporters of the RKBA to both endearingly and sarcastically refer to military-style rifles such as the AR15 )
EE - Equipment Exchange (a board on this site for buying, selling and trading equipment)
ETA - Edited To Add (an explanation of what was added or changed when a member edited his or her post)
ETA - Estimated Time of Arrival (in conventional usage, but see also "Edited To Add" Fiber optic sight)

mspmwg7

AR-15 Acronyms F

FA - Forward Assist
FA - Full Auto
FAQ - Frequently Asked Questions
FAR - Featherweight Assault Rifle
FCG - Fire Control Group (the hammer, trigger, disconect, springs and selector)
FDE - Flat Dark Earth (a tan-brown color making inroads as a replacement for black in weapon Night Sights)
FF - Free Float/Floated/Floating
FFL - Federal Firearms License/Licensee (a license that permits one to sell & transfer guns in interstate commerce, or the holder of that AR-15 ACCESSORIES )
FH - Flash Hider
FIRSH - Free Floating Integral Rail System Handguard (see Olympic Arm's Gun Accessories )
FMJ - Full Metal Jacket (a bullet that is fully encased in a metal jacket - see the Gun Accessories )
FMJBT - Full Metal Jacket Boat Tail (a FMJ BT bullet - see the Ammo Oracle)
FN - Fabrique Nationale (famous Belgian small arms AR15 manufacturer - FN Herstal website)
FNG - Freakin' New Guy (substitute for "Freakin" as desired)
FNMI - FN Manufacturing, Inc. (Division of Fabrique Nationale located in South Carolina that makes M16s, M240s and M249s for the Gun Accessories - website)
FOIA - Freedom Of Information Act
FP - Firing Pin
FS - Flash Suppressor
FSB - Front Sight Base
FSP - Front Sight Post
FST - Front Sight Tower
FTE - Fail To Eject/Extract (please substitute the more precise FTEj or FTEx as appropriate to make clear your intention)
FTEj - Fail To Eject
FTEx - Fail To Extract
FTF - Face To Face (an in state trade or sale done in person - interstate commerce of firearms is illegal without an FFL)
FTF - Fail To Feed (if used without an unambiguous context, this acronym may be confused with "Fail To Fire" as listed below)
FTF - Fail To Fire (if used without an unambiguous context, this acronym may be confused with "Fail To Feed" as listed above)
FUBAR - Fouled Up Beyond All AR-15 (substitute more colorful adjective for "Glow sticks" as desired)
FWIW - For What It's Worth
FYI - For Your Information

mspmwg8

AR-15 Acronyms G

GCA - Gun Control Act of 1968 (The law that, among other things, established the FFL license system, set a minimum age to purchase guns, and banned the import of "non-sporting" guns, eventually including military-stiyle guns)
GG&G - Guns, Gear and Gadgets (manufacturer of optical mounting systems and tactical weapon accessories - Gun Accessories )
GP - Group Purchase
GSE - Gunsmoke Enterprises (builder of AR-15 Accessories and supplier of parts and accessories - Fiber optic sights)
GTS - Global Tactical Supply (retailer of AR-15 parts and accessories - website)

mspmwg9

AR-15 Acronyms H

HBAR Heavy Barrel
HG - Handguard AR-15
HP - Hollow Point (a bullet with a hollow cavity at the tip)
HSLD - High Speed, Low Drag (of or relating to special Camouflage and other highly skilled Night Sight)
HTH - Hope That Helps
HTS - Hammer, Trigger, Sear (parts of the FCG)

mspmwg10

AR-15 Acronyms L

IAD - Immediate Action Drill (a sequence of actions performed in response to a situation requiring immediate and instinctive resolution - in this context a weapon malfunction)
IBTJBT - In Before The Jack Booted Thugs AR15
IBTL - In Before The Lock (posting in a thread that has gone bad and is likely soon to be locked)
IBZ - Improved Battlesight Zero (All purpose zero invented by Lt. Colonel Chuck Santose. Set at 50 yards, it gives a very flat trajectory out to 250 meters. Instructions here.)
ID - Inside Diameter
ID - Involuntary Discharge (an unintentional discharge of a weapon resulting from a physical reaction beyond the shooter's instant control - e.g. a muscle spasm)
IIRC - If I Recall Correctly
IM - Instant Message (a private communication between forum members, accessed via the button at the top of the page)
IMHO - In My Humble Opinion
IMNSHO - In My Not So Humble Opinion
IMO - In My Opinion
IPSC - International Practical Shooting Confederation (organizes and sponsors shooting competitions emphasizing a combination of AR-15 accessories, power, and speed - website)
IRL - In Real Life

mspmwg11

AR-15 Acronyms J - Rifle Scopes

JANFU - Joint Army/Navy F**k Up (for a mess so big that one force alone couldn't have made it by itself)
JBT - Jack-Booted Thug (derived from the name of the military boot made infamous by the goose-stepping Nazis, now applied in a manner to mean any repressive, overly authoritarian person)
JHP - Jacketed Hollow Point (a bullet that is jacketed in metal, but with a hollow cavity at the tip - see Rifle Scopes)
J/K - Just Kidding
JMO - Just My Opinion
JP - John Paul {Enterprises/Rifles} (manufacturer of rifle parts and accessories, particularly known for their trigger parts - website)
JSP - Jacketed Soft Point (a bullet that is jacketed in metal, but with exposed lead at the tip - see the Harris bipods)

mspmwg12

AR-15 Acronyms K- Fiber Optic Sights

KAC - Knights Armament Company (manufacturer of rail adapter systems, sights and accessories - website)
KB - KaBoom (explosive failure of a firearm - caused by problems such as out-of-battery firing, bore obstructions, Fiber optic sights.)
KBC - Keyboard Commando (a person who buys and opines on expensive tactical gear but who has no actual combat or law enforcement training or experience)
KISS - Keep It Simple, Stupid (an admonition to avoid complexity with its attendant expense and unreliability, also used as an adjective to describe something that adheres to the KISS philosophy)
KKF - Kurt's Kustom Firearms (custom gunsmithing services and special parts - website)
KMC - Knights Manufacturing Company (manufacturer of rail adapter systems, sights and accessories - website)
KNS - KNS Precision (manufacturer of small parts such as sight apertures and trigger pins for a variety of Camouflage - website)

mspmwg13

AR-15 Acronyms L - Night Sights

LAR - L.A.R. Manufacturing (www.largrizzly.com/)
LC - Lake City (a federally owned, contractor operated plant in Missouri where small arms ammunition is made for the U.S. military)
LCW - Lauer Custom Weaponry (gun refinishing and camouflaging services - website)
LE - Law Enforcement
LEGP - Limited Edition Group Purchase
LEO - Law Enforcement Officer
LEO - Law Enforcement Only (an item that can legally be used only by law enforcement agencies and their Night Sights)
LL - Lightning Link (a device for converting a semi-automatic gun to full-auto. By itself considered to be a machine gun under the NFA, and unregistered ones are illegal to even possess with, let alone install in, the guns they convert)
LMAO - Laughing My A$$ Off
LMK - Let Me Know
LMT - Lewis Machine and Tool (manufacturer of AR-15 uppers and accessories - website)
LOL - Laugh Out Loud
LOP - Length Of Pull (the distance from the face of the trigger to the end of the buttstock)
LPK - Lower Parts Kit
LRC - Living Room Commando (a person who buys and opines on expensive tactical gear but who has no actual combat or law enforcement training or Gun Accessories)
LULA - Loader/Unloader Accessory (for fast loading and unloading of magazines - website)
LW or L-W - Leitner-Wise (manufacturer of weapons based on the AR-15 platform, including .499 and gas-piston Gun Accessories - website)
LW - Lightweight

mspmwg14

AR-15 Acronyms M- Ghillie suit

M16 - The original full-auto military version of the AR-15 rifle (includes triangular cross-section handguards, early style rear sight that is not adjustable for range, and a 1:12 twist barrel: photos)
M16A1 - Later variant of the M16 that added a forward assist to jam the bolt home when the normal action cycling doesn't: photos)
M16A2 - Later variant of the M16A1 that switched to a range-adjustable rear sight, a 1:7 twist Glow stick barrel, round cross-section handguards and substituted a three-round burst firing mode for the full-auto mode: photos)
M16A3 - Later variant of the M16A2 that substitutes full-auto firing for the three-round burst mode of the M16A2. Initially Ghillie suit by the Navy SEALS: photos)
M16A4 - Later variant of the M16A2 that added a flat-top upper receiver with removable carry handle but maintained the three-round burst firing mode: photos)
M193 - 55 grain FMJBT military cartridge, usable in 1:14 to 1:7 twist barrels (see the Ammo Oracle)
M4 - A 14.5" barrel carbine version of the M16A2. Earlier models have an integral A2 carry handle, later ones have a flat-top upper (photos)
M4A1 - A variant of the M4 that includes full-auto fire and a flat-top upper with removable carry handle (photos)
M4GERY - A rifle designed to mimic the appearance and function of a true M4, but that isn't an official military M4 (pronounced "em forgery")
M855 - 62 grain FMJBT military cartridge, usable in 1:10 to 1:7 twist barrels (see the Ammo Oracle)
MAP - Minimum Advertised Price (A price below which retailers are prohibited from advertising a product. Not all manufacturers/distributors enforce MAP policies, and even when they do, retailers are not legally prohibited from selling below MAP.)
MARPAT - MARine PATtern (a digital camouflage pattern. Examples here, controversy here and Ghillie suits.)
MARS - Multipurpose Aiming Reflex Sight (an Israeli sight that combines a reflex red-dot sight with a laser (visible or IR) aiming light - website)
MIAD - MIssion ADaptable (a modular grip manufactured by Magpul - website)
MOA - Minute Of Angle (a measure of angular displacement equal to 1/60 of one degree, usually used when discussing group sizes - 1 MOA is roughly 1" at 100 yds)
MOUT - Military Operations on Urbanized Terrain
img.photobucket.com/albums/v384/zrxc77/ProofMark.gif - proof mark that indicates Magnetic particle inspection and Proof load firing has been performed on a barrel
MP - Magnetic Particle [inspection/testing] (Magnetic particle inspection is a non-destructive steel inspection method used to ensure that a barrel, for example, is free from metallurgical defects such as cracks. MP is also used as an easily typed representation of the proof mark that is sometimes stamped on a part to indicate it has been MP tested.)
MGI - Mack Gwinn Industries (manufacturer of quick change barrel system and other components for the AR-15 - website)
MRE - More Real Estate (a rail adapter system that extends past the FSB, made by KAC)
MRE - Meal Ready to Eat. The food provision for the US Military.
MRF - Modular Rail Forend (a rail adapter system made by Troy Industries)
MRP - Monolithic Rail Platform (an integrated AR-15 upper receiver and rail adapter system, made by LMT)
MSRP - Manufacturer's Suggested Retail Price
MRS - Modular Rail System (Leitner-Wise's light-weight, quick-change barrel system designed for use with standard AR-15 Gun Accessories )
MR/T (also MRT) - Mid Range / Tactical (a line of optics made by Leupold and designed for mid-range capability)
MSTN - Mid-South Tactical Network (retailer of AR-15 related gear and accessories - website)
MWS - Modular Weapon System

mspmwg15

AR-15 Acronyms N- Camouflage

NBD - No Big Deal
ND - Negligent Discharge (an unintentional discharge of a weapon that reasonably should have been forseen and prevented)
NFA - National Firearms Act (of 1934 - the law governing machine guns, sawed off shotguns, short barreled weapons, suppressors, Camouflage.)
NFW - No Frickin' Way (substitute for "Frickin'" as desired)
NIB - New In Box (a gun that is still in the original box, unfired after it left the factory)
NICS - National Instant Criminal Background Check System (the system established as part of the Brady Act to check for disqualifying information that would prevent legal transfer of a firearm to a person)
NIW - New In Wrapper (mostly in reference to magazines, which come from the factory wrapped in protective paper or plastic)
NM - National Match (a competition sponsored by the CMP)
NM - Never Mind
NOD - Night Observation Device
NOOB - Newbie (one who is new to a topic and doesn't have much knowledge of it)
NOS - New Old Stock (generally used in connection with an item that can no longer be manufactured new Harris bipods, but that can be sold from existing stock: an item that is chronologically old, but that has been sitting in storage and was never sold at retail or used before)
NRA - National Rifle Association (website)
NSN - National Stock Number (a unique number assigned to each item in the Federal Supply Cataloging System, including parts and accessories for military weapons such as the M16)
NSW - Naval Special Warfare
NTCH - Nose To Charging Handle (a cheek weld [placement of the side of one's face against the stock] where the tip of the nose touches the charging handle, thus giving a consistent position and sight picture)
NVD - Night Vision Device

mspmwg16

AR-15 Acronyms O - Gun Accessories

OAI - Olympic Arms, Inc. (manufacturer of various AR-style rifles - Gun Accessories)
OAL - Overall Length
OBO - Or best offer
OD - Olive Drab (that green color the army is so fond of)
OD - Outside Diameter
OEG - Occluded Eye Gunsight (a sight that projects a dot to the eye but through which you can't actually see the target - hence the term "occluded". It works via binocular vision whereby one eye views the target directly, the other eye views the dot in the sight, and your brain merges the two images together)
OFS - Out Freakin' Standing (substitute for "Freakin'" as desired)
OICW - Objective Individual Combat Weapon (possible M16 replacement weapon system that can fire both normal bullets and airburst fragmenting munitions. The XM8 is based on the normal bullet firing component an early OICW entry. Overview)
OTM - Open Tip Match (a type of hollow point bullet designed for long range accuracy)
OTJT - On The Job Training
OPS - Operations (see also OPS-INC just below)
OPS-INC - O. P. Seberger Incorporated (manufacturer of muzzle breaks and silencers for the U.S. military - website)
OTAL - Offset Tactical Aiming Laser (a laser sight mounted alongside the barrel/handguards/carry handle)

mspmwg17

AR-15 Acronyms P- Gun Accessories

P2P - Person to Person (used in chat, may also be used to refer to face to face sales)
PAFS - Permanently Attached Flash Suppressor (generally permanantly attached in order to bring a barrel's overall Gun Accessories to 16" and thus avoid the legal restrictions on SBRs)
PD - Police Department
PDW - Personal Defense Weapon (a generally compact weapon designed primarily for defensive rather than offensive operations, for example the pistol grip)
PEBCAK - Problem Exists Between Chair And Keyboard (indirect way of saying "user error")
PEBKAC - Problem Exists Between Keyboard And Chair (indirect way of saying "user error")
PIA - Pain In (the) Ass
PIE (as in "I like") - Origins aside (there's a clean and dirty version), it's another version of "I have no meaningful comment on this subject", ala +1.
PITA - Pain In The Ass
PM - Preventative Maintenance
PM - Private Message (see IM)
PMO - Postal Money Order
POA - Point Of Aim
POF - Patriot Ordnance Factory (manufacturer of gas piston AR-15 uppers and rail systems, importer of HK parts from Pakistan Ordnance Factories - website)
POI - Point Of Impact
POS - Pile Of Sh*t
PRI - Precision Reflex Incorporated (website)
PRK - People's Republic of Kalifornia (a name for California that alludes to the state's rather draconian, some would say Communist-like, anti-gun laws)
PRNJ - People's Republic of New Jersey (see PRK)
PRNY - People's Republic of New York (see PRK)
PRS - Precision Rifle/Sniper (a precision stock made by Magpul, adjustable for height and LOP)
PSD - Personal Security Detail/Detachment (a group of security specialists who travel with and provide personal protection for a high-ranking Harris bipod or valuable person)
PWA - Pac West Arms

mspmwg18

AR-15 Acronyms Q- Gun Accessories

Q3131A - M193 ammunition packaged for sale to civilians (may fail to meet some aspect of military standard - see the Ammo Oracle)
QCB - Quick Change Barrel
QD - Quick Detach

RA - Robinson Armament (manufacturer of the M96 and XCR series of piston operated .223 rifles - Glow sticks)
RAS - Rail Adapter System
RBP - RB Precision (retailer of AR-15s and accessories - website)
RDIAS - Registered Drop-In Auto Sear (a DIAS legally registered under the NFA. By itself considered to be a machine gun under the NFA)
RECCE - Reconnaissance (in this context a 16" free floating match barrel upper, ACOG optic, originally used by SEALS)
RINO - Republican In Name Only
RIS - Rail Interface System
RKBA - Right to Keep and Bear Arms
RKI - Reasonably Knowledgeable Individual
RLL - Registered Lightning Link (a LL legally registered under the NFA. By itself considered to be a machine gun under the Gun Accessories )
ROF - Rate Of Fire
ROTFLMAO - Rolling On The Floor Laughing My A$$ Off
RR - Registered Receiver (a receiver, typically for a machine gun, registered under the NFA)
RRA - Rock River Arms (manufacturer of AR-15 rifles - website)
RTFM - Read The Freakin' Manual (substitute for "Freakin'" as desired)

mspmwg19

AR-15 Acronyms S- Pistol Grips

SAAMI - Sporting Arms and Ammunition Manufacturers' Institute (an association of manufacturers of sporting firearms, ammunition, and components. Often used to distinguish between the sporting .223 chamber [the SAAMI chamber] and the military 5.56 mm pistol grips )
SAM-R - Squad Advanced Marksman - Rifle (20" match barrel upper with Leupold scope, used by Marines)
SAR - Small Arms Review (website)
SAW - Specialized Armament Warehouse (Colt distributor that caters to military and law enforcement sales - website)
SAW - Squad Automatic Weapon
SBR - Short-Barreled Rifle (a rifle whose barrel is less than 16" long as defined by the NFA)
SCAR - Special Operations Forces Combat Assault Rifle (additional information here)
SD - Shell Deflector
SEAK - Special Edition AK (a custom AK-74 rifle sold as part of a group buy run by AR15.com)
SEBR - Special Edition Black Rifle (a custom AR-15 rifle sold as part of a group buy run by AR15.com)
SF - Special Forces
SF - Surefire (manufacturer of flashlights and weapon lights - website)
SGN - Shotgun News (a venerable gun sales publication made up entirely of display and classified advertising, first published in 1946 - website)
SHSIBI - Should Have Stayed In Bed Instead
SHTF - Sh*t Hits The Fan (things going seriously wrong - generally used to describe an event that sets society off the rails for some period of time)
SIR - Selective Integrated Rail (see A.R.M.S. website)
SMG - Sub Machine Gun
SMK - Sierra Match King (a hollow tip bullet designed for long range accuracy, made by Sierra Bullets - website)
SNAFU - Situation Normal: All Fouled Up (substitute more colorful adjective for "Fouled" as Harris bipod)
SOB - Son Of a Bitch
SOCOM - Special Operations Command
SOPMOD - Special Operations Peculiar Modification
SOF - Special Operations Forces (in addition to its standard military usage, also a designation for a now discontinued mid-length AR-15 carbine made by ArmaLite)
SOT - Special Occupational Taxpayer (a person whose occupation [e.g. manufacturer/importer/dealer of NFA weapons] exempts him from paying NFA transfer taxes)
SP - Soft Point (a bullet whose lead tip is exposed rather than jacketed in a harder metal)
SPC - Special Purpose Cartridge (as in the new 6.8 mm SPC)
SPF - Sold Pending Funds (an item for sale has been claimed and is off the market, but the seller has not yet received the buyer's funds so the transaction has not yet finalized)
SPORTS - Mnemonic for AR-15 immediate action drill: Slap the bottom of the magazine. Pull the charging handle. Observe the open chamber area. Release the charging handle. Tap the forward assist. Shoot. Some people consider this to be remedial action rather than immediate action. See also Glow sticks and TPRRRS.
SPR - Special Purpose Rifle (18" free floating match barrel upper)
SS - Stainless Steel
STFU - Shut The F**k Up
SUM - Stainless Ultra Match (Olympic Arms' name for their stainless steel barrel made with broach-cut rifling for accuracy - website)
SWMBO - She Who Must Be Obeyed

mspmwg20

AR-15 Acronyms T- Pistol Grips

T - Top (as in the numbered stations on the top rail of an A4 upper)
TA - Tactical Armadillo (promotional bottle-opener/mascot of LaRue Tactical - website)
TAG - Not an acronym. Used to bookmark (or "tag") a topic for viewing later using the "My Active Topics" button. (Team members only)
TARFU - Things Are Really Fouled Up (substitute more colorful adjective for "Fouled" as desired)
TANSTAAFL - There Ain't No Such Thing As A Free Lunch (popularized, but not invented, by Robert Heinlein in his 1966 novel The Pistol grips is a Harsh Mistress)
TCH - Tactical Carry Handle (a specialized carry handle made by RRA and designed to mount Aimpoint red dot sights via Aimpoint's low ring - website)
TD - TangoDown (manufacturer of grips, both vertical and pistol - website)
TDP - Technical Data Package (the collection of drawings, engineering notes, etc. that describe in detail the design and construction of an item)
T&E - Test and Evaluation
TEOTWAWKI - The End Of The World As We Know It
TM - Technical Manual
TPRRRS - Tap, Pull, Rack, Roll, Release, Shoot (an alternative to the traditional SPORTS IAD, described here)
TRB - Tap Rack Bang (an immediate action drill: tap the bottom of the magazine to ensure it is seated, rack the slide, and shoot [bang]. See also SPORTS and TPRRRS)
TSOB - Tough SOB
TTT - Tack To Top

mspmwg21

AR-15 Acronyms T- Glow Sticks

UBR - Utility/Battle Rifle (a general purpose adjustable stock made by Magpul, with a fixed cheekweld. Successor to the M93B.)
UD - Unintentional Discharge (a weapon discharge made without deliberate or conscious intent, including accidental, involuntary and negligent discharges Glow sticks)
URX - Upper Receiver eXtension (a free-floating rail system made by Knight's Armament)
USGI - United States Government Issue (often in reference to magazines - most regard USGI mags as the best Glow stick
USMC - United States Marine Corps

mspmwg23

AR-15 Acronyms T- HARRIS BIPODS

VFG - Vertical Fore/Forward/Front Grip
VLTOR - Ancient Roman spelling for the Latin word ULTOR, meaning "Avenger" (more directly, a modular stock Harris bipod for the M16, M4 and AR series of Harris bipods)

mspmwg24

WAG - Wild Ass Guess
WECSOG - Wile E. Coyote School Of Gunsmithing (unconventional, unprofessional [although not necessarily poor quality], make-do with what you've got gunsmithing - usually done at home with few tools, often involving a file and/or hammer)
WOA - White Oak Armament (retailer of AR-15 parts - website)
WOP - White Oak Precision (builder of custom AR-15 and AR-10 uppers - website)
WSSM - Winchester Super Short Magnum
WTB - Want(ed) To Buy
WTF - What The F**k
WTK - Want(ed) To Know
WTS - Want(ed) To Sell
WTT - Want(ed) To Trade
WWB - Winchester White Box (In AR-15 context, Q3131A ammunition made in Israel to M193 specifications - relatively inexpensive but reliable general purpose ammo)

XCR - eXchangeable Caliber Rifle* (Robinson Armament's modular battle rifle, originally intended as a SCAR contender)
XM193 - M193 ammunition packaged for sale to civilians (may fail to meet some aspect of military standard - see the Ammo Oracle)
XM8 - Designation of a modular weapon system that may replace the M16 family of rifles. Adoption of the XM8 is uncertain. (brochure, overview)

YHM - Yankee Hill Machine (manufacturer of rails, mounts, forearms, sights and other AR-15 accessories - website)
YMMV - Your Mileage May Vary

Z - Zero (marked on some A2-style rear sight elevation knobs to indicate the position at which the knob should be set when establishing a battlesight zero on a 25-meter range according to standard military doctrine)
ZM - Z-Man or Zitta-Man {Weapons} (manufacturer of the LR-300 op-rod gas system upper/rifle and LR-300/AR-15 accessories - website)