surefire & harris bipods

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.

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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)