Acronyms and Abbreviations used at AR15.com
Ammo FAQ (Information on .223/5.56, myths, and terminal performance)
Magazine FAQ (question about which magazines to buy, quality, etc)
Bigger Hammer's Colt FAQ
Q: I'm new and I want to know what AR-15 to buy, what do I need to know?
A: This article by juslearnin should be your starting point.
Q: Is .223 the same as 5.56, can I shoot .223 in a 5.56 chamber or vice versa?
A: In short .223 is not the same as 5.56 in chambering - though the ammo dimensionally is identical. Yes you can shoot .223 in 5.56, no you should not shoot 5.56 in .223. For details and explainations why read the Ammo FAQ (above).
Q: How Do I Determine the Round Count on a Used AR I want to buy?
A: Read Bartholomew_Roberts Article n the subject: (not 56K friendly) How To Determine the Round Count of a Used AR-15
Q: How to I keep from losing that little spring when I remove the receiver extension
A: Follow Quarterbore's instructions here
Q: How does the AR-15 gas system work?
A: Read Randall's write up on the gas system
Q: How does the "Piston" in the DI system work (talking about the bolt & bolt carrier)
A: Read bigbore's write up on the bolt & carrier and they work as a piston in the AR
Q: What is the difference between the Mil-Spec and the Commercial Receiver Extensions ('buffer tube')? Who uses what?
A: The commercial tubes are slightly larger in diameter where the stock slides, but slightly smaller in diameter when it screws into the receiver. Either can be installed on standard lowers, with the Mil-Spec one actually having the stronger interface (more surface area of the threads engage the receiver).
Mil-Spec ( 1.148" outer diameter): Colt, LMT, CMT (Stag, S&W, CMMG), VLTOR
Commercial (1.168" outer diameter): Everyone Else (Bushmaster, RRA, DPMS, Olympic, etc.)
Another way to tell is a commercial tube is the same outside diameter as the points on the threads. A milspec size tube is smaller in diameter than the points on the threads so you can see where the threads taper down in size.
Q: I hear a 'SPRONG' kind of noise when I shoot my AR - is something wrong? How do I get rid of it?
A: The noise is perfectly normal. It indicates the weapon is functioning and you'll be able to tell when it's time to change magazines by the change in sound. Of course if you're shooting under stress you won't notice it at all.
To get rid of the sound try using earplug instead of ear muffs. The hard case of the ear-muffs seems to transmit the sound better. Also, some have suggested using grease on the spring to dampen the sound, proper lubrication with CLP works as well.
Q: My A2's (or detachable carry handle) rear sight is crooked, is there a problem?
A: No, that is perfectly normal. While the amount of cant varies, as long as you can zero you're good to go. The sight is designed to have some play to allow it to operate in less than ideal conditions, a spring ensures the sight's aperture will always be the same axis.
Q: I want to work on my AR (change stock, fix something, replace barrel etc). Where can I find out how?
A: First think you need to do is download the '-23&P' Unit & Direct Support Maintenance Manual. You can download it in .PDF format it from this site :Unit & Direct Support Maintenance
Then you need to head to the Build It Yourself
forum and read the tacked threads for tips & tricks on how to do things. The forum even covers free float tubes, which the -23 does not.
Q: I have questions on Ammo, Terminal Ballistics, Which Bullet is best (for defense, for target work, for my twist rate)
A: Please visit the FAQs in our Ammo Forum http://www.ar15.com/forums/forum.html?b=3&f=16
Q: What Range to I zero my rifle for? How do I zero?
A: That's a question where you can get a variety of answers. One of the most popular options is the 50y / 200M Improved Battle Sight Zero
which gives a nice flat trajectory (bullet stays within 2" of the point of aim out to 240 yards or so), yet still calibrates the elevation wheel for you carry handle users. There is also the US Army 25M Zero
, and the 36y/300M zero the USMC uses. Most users of Aimpoints & EOTechs zero them at 50y for a 200M zero with a flat trajectory.
Q: I was 'hand cycling' some ammo and I noticed my primers were dimpled - is this a problem?
I notice a round I ejected from the chamber had a dimpled primer - OMG is this a potential slam-fire !?
A: Relax, that is perfectly normal for a rifle that does not have a spring loaded firing pin. This sort of issue can also be see on other rifles with a floating firing pin
Q: What are 'M4 Feedramps' and how do I know if I have them?
A: They are the feed ramps introduced with the M4 carbine that improved feeding with the M855 round - especially when the magazines were dirty/worn. Unlike previous ARs, these ramps continue onto the upper receiver - see the images below.
(images courtesy of Randall from AR15Barrels.com)
Q: I'm interested in an AR in a caliber OTHER than .223/5.56 where can I find out more?
A: For other calibers we have specific areas of this site setup. Many popular calibers even have FAQs tacked up in the top of these forums.
If you are interested in .22 LR or Pistol Caliber uppers (.22LR, 9mm, .40, .45 etc) visit the Rimfire and Pistol Caliber Forum
If you are interested in other intermediate & wildcat calibers (5.45x39, 6.8 SPC, 6.5 Grendel, .300 Whisper, 7.62x39, .458 SOCOM, .50 Beawulf etc) then visit the AR Variants Forum and check out the FAQs there
Finally, if you're looking for .308 ARs and other calibers based on that case then there are two places you can look.
Q: How many calibers can I get uppers that fit my .223 (AR-15) lower? What are they?
A: While the list is nearly endless with all the wildcats possible. Here are the some of the more common and more interesting uppers that are (or have been) produced for the standard AR-15 lower:
223/5.56 and based upon that case
6 x 45
7 x 40
357 Mag Rimless
300 Whisper / .300Fireball / 300-.221
6.5 x 40
.30 Coyote (30 x 45)
.17 Mach IV
5.7 FN (developed by Rhinland Arms - no word yet on who is going to mfg it)
10 mm Mag
7.62 x 40
7.62 x 39
.338 x 39
6.5 Grendel / 6.5 AR / 6.5 PPC Improved
7 sCAR ....
5.45x39 / .21 Ghengis
8mm (belt fed upper)
.308 (again a belt fed upper - no longer available)
.50 BMG (single shot)
.50 Blackpowder (1 made)
With thanks to Marty at Teppu-Jitsu for starting this list.