AR-15

AR-15
AR-15 SP1
The AR-15 comes in many sizes and has many options, depending on the manufacturer.
Type Semi-automatic rifle / Service rifle
Place of origin  United States
Service history
In service 1958–present
Production history
Designer Eugene Stoner
Designed 1957
Manufacturer ArmaLite, Colt, and others.
Specifications
Weight 2.27 kg–3.9 kg (5.5–8.5 lb)
Barrel length
  • 20 in (508 mm) standard
  • 16 in (406 mm)
  • 14.5 in (368 mm)
Cartridge .223 Remington, 5.56 NATO
Action Direct impingement / Rotating bolt
Rate of fire 800 rounds/min (fully automatic versions only)[1][2][3]
Muzzle velocity 975 m/s (3,200 ft/s)[4]
Effective range 400-600 m (avg 547 yd)[5][6][7]
Feed system Various STANAG magazines.
Sights Adjustable front and rear iron sights

The AR-15 (ArmaLite Model 15[8]) is a widely owned[9] semi-automatic rifle, of which the most famous derivative is the selective fire M16-series assault rifle used by the United States military.

The AR-15 consists of separate upper and lower receiver assemblies, which are attached with two through-pins and can be quickly interchanged with no tools. The lower receiver (because it bears the weapon's serial number and fire control group) is itself regulated as a firearm. However, the upper receiver assembly is simply considered a part, and may be purchased and mail-ordered in most locations with no restrictions. This is an attractive feature for users because it allows a number of upper receivers (often in different calibers) to be interchanged with the same lower receiver.[10] However, one must be thoroughly familiar with firearms laws before doing this as it is possible to make an illegal configuration.[11]

Standard AR-15 rifles accept detachable magazines of widely varying capacities (Including, amongst others, 10, 20, or 30 round box magazines, or 100 round drums), and have a pistol grip that protrudes beneath the stock. AR-15 rifles are highly configurable and customizable. They are commonly fitted with several accessories such as bipods, collapsing stocks, threaded barrels for the attachment of a flash suppressor, and a rail system for the attachment of vertical grips, flashlights, laser sights, telescopic sights and other accessories. The most common bipod is the folding bipod, but here is also a vertical grip with a bipod release. Barrels can come in chrome and stainless steel. The steel barrel tends to be more accurate while the chrome tends to be more durable. You can also get a barrel with a various rates of twist. The smaller the ratio the faster the bullet spin before coming out the barrel; the specific rate of twist is tailored to the desired bullet weight (heavier/longer bullets require more twist). AR-15's can also be assembled with a suppressor.

Contents

History

The AR-15 is based on the 7.62 mm AR-10, designed by Eugene Stoner of the Fairchild ArmaLite corporation.[8] The AR-15 was developed as a lighter, 5.56 mm version of the AR-10. The "AR" in AR-15 comes from the ArmaLite name. ArmaLite's AR-1, AR-5, and some subsequent models were bolt action rifles, the AR-7 a semiautomatic survial rifle and there are shotguns and pistols whose model numbers also include the "AR" prefix.[8]

1973 Colt AR-15 SP1 rifle with 'slick side' upper receiver (no forward assist) and original Colt 20 round box magazine

ArmaLite sold its rights to the AR-10 and AR-15 to Colt in 1959. Colt marketed the AR-15 rifle to various military services around the world, including the U.S. Navy, Air Force, Army, and Marine Corps. The AR-15 was eventually adopted by the United States military under the designation M16. However, Colt continued to use the AR-15 trademark for its semi-automatic variants (AR-15, AR-15A2) which were marketed to civilian and law-enforcement customers. The original AR-15 was a very lightweight weapon, weighing less than 6 pounds with empty magazine, though later heavy-barrel versions of the civilian AR-15 can weigh upwards of 8.5 lbs.[12]

Today the AR-15 and its variations are manufactured by many companies and have captured the affection of sport shooters and police forces around the world due to their accuracy and modularity. (Please refer to the M16 for more history on the development and evolution of the AR-15 and derivatives.)

The trademark "AR15" or "AR-15" is registered to Colt Industries, which maintains that the term should only be used to refer to their products. Other AR-15 manufacturers make AR-15 clones marketed under separate designations, although colloquially these are sometimes also referred to by the term AR-15.

Some notable features of the AR-15 include:

AR-15 sight picture

Semi-automatic AR-15s for sale to civilians are internally quite different from full automatic versions for sale to law enforcement and military customers, though nearly identical in appearance. The hammer and trigger mechanisms are of a different design. The bolt carrier and internal lower receiver of semi-automatic versions are milled differently, so that the firing mechanisms are not interchangeable. This was done specifically to satisfy BATF requirements that civilian weapons may not be easily convertible to full-automatic. Despite this, through use of a "Drop In Auto Sear" or "lightning-link," conversion to full automatic is very straightforward (sometimes requiring slight modification to the bolt carrier).[13][14] Such modifications, unless using registered and transferrable parts made prior to May 19, 1986, are illegal. (The Firearm Owners Protection Act in 1986 has redefined a machinegun to include individual components where a semiautomatic firearm can be converted to full-automatic based on a 1981 BATF ruling on machinegun parts.) An illegally converted full automatic AR-15 was used in the North Hollywood shootout.

Automatic variants have a three-position rotating selective fire switch, allowing the operator to select between three modes: safe, semi-automatic, and either automatic or three round burst, depending on model. Civilian AR-15 models do not have three-round burst or automatic settings on the fire selector. In semi-automatic only variants, the selector only rotates between safe and semi-automatic. Due to this, weapons modified to full automatic using a lightning-link are capable of full automatic fire only unless a full automatic fire select switch is substituted.[13]

Operating mechanism

Diagram of an M16 rifle, firing

The mechanism of operation for the rifle is known as direct gas impingement. Gas is tapped from the barrel as the bullet moves past a gas port located above the rifle's front sight base. The gas rushes into the port and down a gas tube, located above the barrel, which runs from the front sight base into the AR-15's upper receiver. Here, the gas tube protrudes into a “gas key” (bolt carrier key) which accepts the gas and funnels it into the bolt carrier. The bolt and bolt carrier together form a piston, which is caused to expand as the cavity in the bolt carrier fills with high pressure gas. The bolt is locked into the barrel extension, so this expansion forces the bolt carrier backward in line with the stock of the rifle. As the bolt carrier moves toward the butt of the gun, the bolt cam pin, riding in a slot on the bolt carrier, forces the bolt to turn and unlock from the barrel extension. Once the bolt is fully unlocked it begins its rearward movement along with the bolt carrier. The bolt's rearward motion extracts the empty cartridge case from the chamber, and as soon as the neck of the case clears the barrel extension, the bolt's spring-loaded ejector forces it out the ejection port in the side of the upper receiver.

STANAG magazine compatible with the AR-15. Can be used in many other firearms such as the FN F2000, the M16 and more.

Behind the bolt carrier is a plastic or metal buffer which rests in line with a return spring that pushes the bolt carrier back toward the chamber. A groove machined into the upper receiver traps the cam pin and prevents it and the bolt from rotating into a closed position. The bolt's locking lugs then push a fresh round from the magazine which is guided by feed ramps into the chamber. As the bolt's locking lugs move past the barrel extension, the cam pin is allowed to twist into a pocket milled into the upper receiver. This twisting action follows the groove cut into the carrier and forces the bolt to twist and “lock” into the barrel’s unique extension.

Variants

Colt AR-15 Sporter SP1 Carbine

The AR-15 rifle is available in a wide range of configurations from a large number of manufacturers. These configurations range from short carbine-length models with features such as adjustable length stocks and optical sights, to heavy barrel models.

Due to the rifle's modular design, one upper receiver can quickly and easily be substituted for another. There are many aftermarket upper receivers that incorporate barrels of different weights, lengths and calibers. Some available calibers for the AR-15 platform are the .223 Remington/5.56x45mm, .45 ACP, 5.7x28mm, 6.5 mm Grendel and 6.8 mm Remington SPC.[15] Care must be taken not to chamber the 5.56x45 NATO into a rifle designated 223 Remington, due to different Neck profiles on the 5.56mm cartridges, the two calibers are similar, but not identical.

When installing a new complete upper receiver, particularly one designed to handle a different caliber of ammunition (i.e., other than .223 Remington or 5.56x45 mm NATO), some modification to the contents of the lower receiver may also be required, depending on the particular conversion. For example, a conversion to 9 mm typically would involve the installation of a magazine well block (to accommodate a typical 9 mm magazine, such as Uzi or Colt SMG), replacing the .223 hammer with one designed for 9 mm ammunition, and depending on the original stock, replacing the buffer, action spring and stock spacer with those designed for the new 9 mm AR-15 configuration.

Colt AR-15 A3 Tactical Carbine. Rifle is shown with a CQB Tactical Sling and a Colt 4x20 scope.

Early models had a 1:14 rate of twist for the original 55 grain (3.6 g) bullets. This was changed to 1:12 when it was found that 1:14 was insufficient to stabilize a bullet when fired in cold weather. Most recent rifles have a 1:9 or 1:7 twist rate. There is much controversy and speculation as to how differing twist rates affect ballistics and terminal performance with varying loads, but heavier projectiles tend to perform better with faster rifling rates.[16] Additionally, the various non .223 / 5.56 calibers have their own particular twist rate, such as 1:10, 1/11 and 1/12 for 6.8x43mm SPC, 1/10 7.62x39mm, and 1:12 for .308 Winchester.

A Colt AR-15 on display at the National Firearms Museum.

Standard issue magazines are 20 or 30 round staggered-column magazines, traditional box magazines also exist in 40 and 45 round capacities, and usable magazines have been constructed from a variety of materials including steel, aluminum, and high-impact plastics. Drum magazines with 90 and 100 round capacities also exist, such as Beta C-Mags. Low-capacity magazines, usually of a 5 or 10 round capacity, are available to comply with some areas' legal restrictions, hunting and because larger magazines can inhibit shooting from a benchrest.

Legal status

Australia

AR-15 rifles, like all semi-automatic rifles, are banned from legal ownership in all states and territories in Australia. The ban on semi-automatic rifles was introduced in 1996 in response to the Port Arthur massacre, in which 35 people were killed. The main weapon used in the attack was an AR-15. The only way a private, law-abiding Australian citizen can legally own an AR-15/M16-type rifle in Australia today is to have a Firearms Collector's Licence and the firearm deactivated (with the barrel plugged up and the action welded shut) or to have a Category C/D Firearms Licence if they are a professional animal culler or a primary producer. Before the 1996 gun laws, AR-15 rifles were legal in a number of states and territories of Australia with the states of Queensland and Tasmania being prime examples.

Canada

The Government of Canada classifies the AR-15 (and its variants) as a restricted firearm. For anyone wanting to lawfully own an AR-15, they must first pass a "Canadian Non-Restricted Firearms Safety Test", and then a "Canadian Restricted Firearms Test". This allows the applicant to obtain a Possession and Acquisition Licence (PAL) valid for restricted firearms, subject to approval.[17][18] With the introduction of strict gun control measures by former Prime Minister Jean Chrétien (Bill C-68), the AR-15 had originally been intended to be classified as a prohibited firearm, making it all but impossible to privately own one, however due to the presence of nationwide Service Rifle target shooting competitions, the AR-15 was granted a sporting exception.

As with all Restricted firearms (including all pistols, some shotguns, and some rifles) AR-15s are only allowed to be shot at certified firing ranges. In order to legally own and transport a Restricted firearm, the firearm must be registered with the Royal Canadian Mounted Police Canadian Firearms Program and must apply for an Authorization to Transport (or ATT) from the Chief Firearms Officer (CFO) for their province or territory. Additionally, the firearm must be unloaded, deactivated by a trigger or action lock, and be in a locked, opaque container during transport.[19]

The issuance of ATTs varies considerably from province to province, and is generally reflective of a particular province's political and social levels of acceptance toward gun ownership. For example, in Alberta, where firearms ownership is widely accepted, generally a single ATT is promptly issued that allows citizens to transport firearms to border crossings, gunsmiths, and shooting ranges.

Germany & Finland

In Germany and Finland, possession of semi-automatic rifles, including the AR-15, is legal, provided that the rifle's owner acquires a permit for owning one. However, in order for someone to own a rifle in these countries, whether it is semi-automatic or single shot, there needs to be a specific reason. Participation in the shooting sports and hunting are valid reasons for obtaining a license to buy a firearm. A license is required for each individual firearm.

Austria

In Austria the possession of semi-automatic centerfire rifles, except military rifles (e.g. M1 Garand, SKS rifle etc.), is generally legal for persons, who own a gun license (there are two: "Waffenbesitzkarte" and "Waffenpass"). Only such semi-automatic rifles are legal, that are made by a civilian arms manufacturer and are intended for sporting and hunting purposes and are licensed by the Austrian ministry of interior. Currently only one AR-15 version by the civilian German sporting arms manufacturer "Oberland Arms" could attain such a license for a rifle called OA-15-Austria. The Austrian version has some minor differences to the German OA-15 rifle in order to pass Austrian gun laws, which not only forbid possession of military semi-automatic rifles, but also forbid the possession of barrels and bolts, that could be used in these rifles. Therefore the OA-15-Austria's bolt has only 6 locking lugs instead of 7. The barrel has been modified, so original military AR-15 bolts with 7 locking lugs cannot be used. The bolt carrier has also been modified to make it difficult to convert the rifle into a fully-automatic rifle. Additionally the mounting of flash hiders and bayonet lugs on semi-automatic rifles is prohibited.

United Kingdom

As with all semi-automatic, centerfire rifles, AR-15s are classed as a Section 5 weapon (i.e. a person must provide an exceptional reason and gain permission from the Home Secretary making ownership all but impossible for a private citizen) however AR-15s in a manually operated straight pull configuration or semi-automatic AR-15s that are chambered to fire a .22 rimfire cartridge are legal and can be held on a standard Section 1 Firearms Certificate. There are no restrictions on 'assault weapon features' in the UK, however magazines are limited to 10 rounds. There are a number of UK manufacturers of "straight-pull" AR-15 variants, the Bradley Arms BAR-15 being widely respected as it is becoming the competition AR variant of choice amongst the Civilian Service Rifle community. Southern Gun Company has tried to introduce a 9mm "self-ejecting" variant for gallery rifle shooting nicknamed the "Unicorn" but, despite numerous units being sold on the understanding the rifle was a compliant Section 1 firearm, the rifles were seized and subjected to stringent testing by the UK licensing authority's Forensic Science Services (FSS). A small number of pre-production models were found to be non-compliant with section 1 status. However, later models were deemed Section 1 compliant and were returned to their owners.

United States

In the United States, variants with certain features such as collapsible stocks, flash suppressors, and bayonet lugs were prohibited for sales to civilians during the period 1994–2004 by the Violent Crime Control and Law Enforcement Act of 1994, under the provision known as the Assault Weapons Ban. Included in this was a restriction on the pistol grip that protrudes beneath the stock, which was considered an accessory feature under the ban and was subject to restrictions. Some rifles were manufactured with a grip not described under the Ban installed in its place. Those AR-15s that were manufactured with those features were stamped, "Restricted Military/Government/Law Enforcement/Export Only" as well as the accompanying full capacity magazines. Since the expiration of the Federal AWB in September 2004,[20] these features are now legal in most states.[21] The above restrictions only applied to guns manufactured after the ban took effect. It was legal to own, sell, or buy any gun built before 1994. Hundreds of thousands of pre-ban ARs were sold during the ban as well as new guns redesigned to be legal.

Assembling a short barreled AR-15

Under U.S. firearms laws, only the lower receiver of the AR-15 is considered a firearm and subject to purchasing restrictions. (This is not universally the case with rifles. On some other rifles, such as the FN FAL, the upper is the serial-numbered part, and thus the firearm.) The upper receiver assembly is simply considered a part, and may be freely purchased and mail-ordered in most locations. This is a very attractive feature for enthusiasts, who can purchase a number of upper receivers (often in different calibers) and interchange them with the same lower receiver. However, one must be thoroughly familiar with firearms laws before doing this as it is possible to make a configuration that requires a special approval or tax stamp or a configuration that is illegal under state law.

For example, an 11" barrel with only a pistol grip is a legal handgun in most locations. Adding a shoulder stock to an AR-15 with a barrel shorter than 16" would constitute constructing a Short-Barreled Rifle (SBR) under NFA rules - subjective to a $200 tax stamp. Constructing an AR-15 pistol using a lower receiver which had already been designated a rifle or described as such on an ATF form 4473 would constitute the construction of a firearm, since the pistol was constructed from an existing rifle. It is a felony to assemble, possess, or transfer such a weapon without obtaining ATF approval (subject to state approval) and the corresponding $200 tax stamp. If a lower receiver is designated and transferred as a pistol, you are disallowed from installing a butt stock or a forward pistol grip, as the former would render it an SBR (short barreled rifle), with the latter effectively constructing an AOW (Any Other Weapon) requiring the ATF approval and tax stamp.

California

A California-legal AR-15 clone (FAR-15) with a 10 round magazine. Other notable features include pinned and welded muzzle brake, forward assist, "Bullet Button", collapsible stock & M68 (sight optic) mounted on the top rail.

The 2000 Assault Weapons ban in the state of California sparked a renewed interest in the AR-15 rifle. It is estimated that some 400,000 California Legal AR-15s are in existence in that state, with another 100,000 added each year.[22] There are three ways to get a legal AR-15 in California:

  1. Registered Assault Weapon: If you owned the rifle before Jan 1, 2000 and registered it with the state, you have a Registered Assault Weapon (RAW) under CA law. No new registrations are permitted. RAW rifles can have combinations of features which are prohibited in unregistered rifles.
  2. Fixed Magazine Rifle: This style of rifle is made by combining an AR-15 upper receiver with an AR-15 lower receiver which has not been specifically banned by name, and which has a fixed 10-round (maximum) magazine. In such a configuration, the rifleman could add otherwise prohibited features such as a telescoping stock and pistol grip. The magazine is not detachable, so to load the rifle the shooter must either "top load" or use a magazine lock. To top-load, the shooter pulls the rear takedown pin, hinges the upper receiver on the front pivot pin, and loads the now exposed magazine. Several devices are available on the market which replace the magazine release button with an inset pin that requires the use of a special tool to activate the magazine release.
  3. Featureless Rifle: If a rifle has none of the prohibited features (pistol grip, telescoping or folding stock, flash hider, grenade/flare launcher, forward pistol grip), the rifle may be used with legally-owned large capacity magazines. There are several products available on the market to configure featureless rifles. Special grips are available which prevent the thumb from going behind it as would be the case with a pistol grip configuration. They are therefore not a prohibited wrap-around style grip. Separate buffer tubes to contain the recoil spring and buffer assembly may also be used in conjunction with special stocks without prohibited grips or stock adapters which attach to the pistol grip mount.

Most AR-15 manufacturers now make lower receivers which qualify as "Off-List" Lowers (OLL) in the state of CA.

Caution

With the plethora of manufacturers of complete weapons and aftermarket barrels, there is a potential hazard associated with chamber specifications. Both civilian (SAAMI) specification .223 Remington and 5.56 mm NATO are available. Though both chambers typically accept both types of ammunition, the firing of military specification ammunition in civilian specification chambers can produce chamber pressures greater than the barrel is designed to handle. The most common result of firing military 5.56x45mm ammunition in a .223 Remington chamber is that the primer can be forced out of the case by chamber pressure, often resulting in the primer becoming lodged somewhere in the action of the rifle, and disassembly of the rifle is often necessary to remove the jammed primer.[23] Military specification chambers typically have a more open throat area producing less pressure and can handle both types of ammunition.

A few AR-15 manufacturers incorporate the use of a hybrid chamber specification known as the Wylde chamber. Designed by and named after Bill Wylde, this chambering was designed to accurately shoot the military ball ammo of the day while still feeding reliably. Coincidentally, it shoots the longer 80 gr bullets commonly used in the sport of Highpower Rifle Competition very well and is one of the preferred chambers for that use. While the Wylde chamber allows for optimal seating depth of 80 grain bullets over .223 Remington and 5.56 NATO, it is capable of accepting both ammunition types. The Wylde chamber is used by a few manufacturers who sell "National Match" configuration AR-15 rifle, barrels, and upper receivers.

The type of chamber, manufacturer, and rifling twist in inches is typically found stamped into the barrel in front of the front sight assembly.

An additional point of concern in the design is the inertial firing pin. A lightweight firing pin rides in a channel inside the bolt unrestrained. When the bolt locks forward during loading, the firing pin typically rides forward and impacts the primer of the chambered round. In military specification ammunition and quality civilian ammunition, this is not normally enough to fire the round and only leaves a small "ding" on the primer. With more sensitive primers or improperly seated primers, this can cause a slamfire during loading.[24]

See also

  • C7
  • T65 assault rifle
  • Bushmaster M4 Type Carbine

References

  1. ↑ "M-16 Rifle also called AR-15". http://www.britannica.com/EBchecked/topic/353341/M16-rifle. Retrieved 2008-07-16. 
  2. ↑ "Infantry Weapons Used in Borneo". http://www.britains-smallwars.com/Borneo/borneo-weapons.html. Retrieved 2008-07-16. 
  3. ↑ "M-16/AR-15". http://www.websters-online-dictionary.com/definition/AR-15%252FM16. Retrieved 2008-07-16. 
  4. ↑ "Armalite AR-15". http://www.probertencyclopaedia.com/cgi-bin/res.pl?keyword=Armalite+AR-15&offset=0. Retrieved 2008-07-16. 
  5. ↑ "Colt AR-15". http://www.coldwarshooters.net/index.php?main_page=product_info&cPath=11&products_id=627. Retrieved 2008-07-16. 
  6. ↑ "ARMALITE AR-15". http://www.probertencyclopaedia.com/F_ARMALITE_AR-15.HTM. Retrieved 2008-07-16. 
  7. ↑ "Colt Model AR6721". http://www.eastcoastfirearms.com/sub/page.asp?page_id=42. Retrieved 2008-07-16. 
  8. ↑ 8.0 8.1 8.2 "A Historical Review of Armalite" (PDF). ArmaLite, Inc.. 1999-04-23. http://www.armalite.com/images/Library/AL%20HISTORY%20COPY%202.pdf. Retrieved 2008-07-16. 
  9. ↑ Lou Dobbs (anchor); David Olofson (gun owner). (2008-07-02) (swf). Lou Dobbs Tonight: Freedom Under Fire. [News]. CNN. Event occurs at 00:01:34. http://www.cnn.com/video/#/video/bestoftv/2008/07/02/ldt.tucker.olofson.jail.cnn?iref=videosearch. Retrieved 2008-07-03. "That conviction has drawn attention among gun enthusiasts, because it centers on a rifle that is widely owned —- the AR-15." 
  10. ↑ U.S. Military Small Arms Ammunition Failures and Solutions, GK Roberts, NDIA Dallas, TX, 21 May 2008 http://www.dtic.mil/ndia/2008Intl/Roberts.pdf
  11. ↑ Gunsmithing Rifles, Patrick Sweeney (1999) p. 286
  12. ↑ "AR-15 Carbine". http://www.olyarms.com/index.php?page=shop.product_details&flypage=shop.flypage&product_id=17&category_id=7&manufacturer_id=0&option=com_virtuemart&Itemid=37&vmcchk=1&Itemid=37. Retrieved 2008-07-16. 
  13. ↑ 13.0 13.1 "Lightning Link Page". http://www.quarterbore.com/nfa/lightninglink.html. Retrieved 2009-05-10. 
  14. ↑ "Drop in Auto-Sear Page". http://www.quarterbore.com/nfa/dias.html. Retrieved 2009-05-10. 
  15. ↑ U.S. Military Small Arms Ammunition Failures and Solutions, GK Roberts, NDIA Dallas, TX, 21 May 2008 http://www.dtic.mil/ndia/2008Intl/Roberts.pdf
  16. ↑ Miller, Don. How Good Are Simple Rules For Estimating Rifling Twist, Precision Shooting - June 2009
  17. ↑ Firearms Safety Training, Canadian Firearms Centre (CFC)
  18. ↑ List of Restricted and Prohibited Firearms, Canadian Firearms Centre (CFC)
  19. ↑ "RCMP Firearms Program Regulations on Transporting Firearms". Rcmp-grc.gc.ca. 2007-04-20. http://www.rcmp-grc.gc.ca/cfp-pcaf/faq/trans-eng.htm#d1. Retrieved 2009-11-28. 
  20. ↑ "ATF Online — Firearms FAQs (section O, question 1)". ATF. 2006-07-06. http://www.atf.gov/firearms/faq/faq2.htm#o2. Retrieved 2007-01-23. 
  21. ↑ "ATF Online — Firearms FAQs (section O, question 11)". ATF. 2006-07-06. http://www.atf.gov/firearms/faq/faq2.htm#o11. Retrieved 2007-01-23. 
  22. ↑ "The California Firearms Enthusiast's Home On The Internet". calguns.net. http://www.calguns.net/calgunforum/showthread.php?t=214851. Retrieved 2009-11-28. 
  23. ↑ "ArmaLite, Inc. Technical Note - 5.56 NATO vs SAAMI .223 Chambers". ArmaLite, Inc.. 2002-12-04. http://www.armalite.com/library/techNotes/tnote45.htm. Retrieved 2007-01-23. 
  24. ↑ "ArmaLite, Inc. Technical Note — Prevention of Slamfires". ArmaLite, Inc.. 1998-12-26. http://www.armalite.com/images/Tech%20Notes%5CTech%20Note%2010,%20Prevention%20of%20Slamfires%20981226.pdf. Retrieved 2009-02-19. 

External links

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