Editing Colt AR-15 (section)

==Features==
[[File:Colt AR-15 Sporter Lightweight rifle - upper lower break (8378298627).jpg|thumb|AR-15A2 with the upper and lower receiver opened at the front hinge]]
[[File:Colt AR-15 Sporter Lightweight rifle - upper handle (8378298701).jpg|thumb|The AR-15A2's most distinctive ergonomic feature is the carrying handle and rear sight assembly on top of the receiver.]]

===Upper receivers===
The upper receiver incorporates the hand guard, the charging handle, the forward assist, the gas operating system, the barrel, the bolt and bolt carrier assembly. AR-15s employ a modular design. Thus one upper receiver can quickly and easily be substituted for another. Upper [[Receiver (firearms)|receivers]] are available with barrels of different weights, lengths, calibers, and rail systems with various sights and accessories. The standard AR-15 rifle uses a {{convert|20|in|adj=on}} barrel. Although, both shorter {{convert|16|in|adj=on}} carbine barrels and longer {{convert|24|in|adj=on}} target barrels are also available.

Early models had barrels with a 1:12 [[Rifling|rate of twist]] for the original .223 Remington, {{convert|55|gr|adj=on}} bullets. Current models have barrels with a 1:9 or 1:7 twist rate for the [[5.56×45mm NATO]], {{convert|62|gr|adj=on}} bullets.

===Lower receivers===
The lower receiver incorporates the magazine well, the pistol grip, the [[Stock (firearms)|buttstock]], the buffer and the buffer spring. The lower receiver also contains the trigger, disconnector, hammer and fire selector (collectively known as the [[fire control group]]). Full-sized rifles use a fixed buttstock, while carbines generally use an adjustable telescoping buttstock.

The early commercial SP-1 AR-15s used a pair of {{convert|0.250|in|adj=on}} diameter receiver push pins, identical to those found on the military rifles. In 1966 the company replaced the front pin with a paired nut and screw hinge using a {{convert|0.315|in|mm|adj=mid|-diameter}} pin to prevent shooters from being able to change receivers with military rifles or competitor rifles without the use of an adapter. They resumed production with the smaller and standardized 0.250-inch pin in the mid-1990s.<ref name="Sweeney1999">{{cite book|last=Sweeney|first=Patrick|title=Gunsmithing - Rifles|url=https://books.google.com/books?id=Eul8bA4KSCcC&pg=PA290|date=1 October 1999|publisher=Gun Digest Books|location=Iola, Wisconsin|isbn=0-87341-665-1|page=290}}{{Dead link|date=December 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

===Sights===
The AR-15's most distinctive ergonomic feature is the carrying handle and rear sight assembly on top of the receiver. This is a by-product of the original [[ArmaLite]] design, where the carry handle served to protect the charging handle.<ref name=SAOW2>{{Cite book |last=Ezell |first=Edward Clinton |title= Small Arms of the World |year= 1983 |publisher= Stackpole Books |location=New York |isbn=978-0-88029-601-4 |pages=746–762|url=https://archive.org/details/smallarmsofworld0000ezel_12ed}}</ref> As the line of sight is {{cvt|2.5|in|1}} over the bore, the AR-15 has an inherent [[Parallax#In gunfire|parallax]] problem. At closer ranges (typically inside 15–20 meters), the shooter must compensate by aiming high to place shots where desired. The standard AR-15 rifle has a {{convert|500|mm|adj=on|2|abbr=in}} sight radius.<ref name=archive_mil>{{cite web |url=http://www.colt.com/mil/M16_2.asp |title=M16 5.56mm Rifle |access-date=2012-10-07 |url-status=dead |archive-url=https://web.archive.org/web/20110616211557/http://www.colt.com/mil/M16_2.asp |archive-date=June 16, 2011 |df=mdy-all }}. colt.com. Retrieved on 8 October 2011.</ref> The AR-15 uses an L-type flip, aperture rear sight and it is adjustable with two settings, 0 to 300 meters and 300 to 400 meters.<ref name=archive.org>{{Cite book|last=United States Government (ARMY)|url=http://archive.org/details/OperatorsManualForM16M16a1|title=Operator's Manual For M16, M16A1|language=English}}</ref> The front sight is a post adjustable for elevation. The rear sight can be adjusted for windage. The sights can be adjusted with a bullet tip or pointed tool. The AR-15 can also mount a scope on the carrying handle. With the advent of the AR-15A2, a new fully adjustable rear sight was added, allowing the rear sight to be dialed in for specific range settings between 300 and 800 meters and to allow windage adjustments without the need of a tool or cartridge.<ref name="Venola, Richard 2005">Venola, Richard (2005). "What a Long Strange Trip It's Been". Book of the AR-15 1 (2): 6–18.</ref> Current versions such as AR-15A4 have a detachable carrying handle and use [[Picatinny rail]]s, which allows for the use of various scopes and sighting devices.

===Muzzle devices===
Colt AR-15 rifles most often have a barrel threaded in {{frac|1|2}}″-28 threads to incorporate the use of a muzzle device such as a [[flash suppressor]], [[sound suppressor]] or [[muzzle brake]]. The initial design, the "duckbill," had three tines or prongs and was prone to breakage and getting entangled in vegetation. The design was later changed to close the end to avoid this problem. Eventually, on the A2 version of the rifle, the bottom port was closed to reduce muzzle climb and prevent dust from rising when the rifle was fired in the prone position.<ref name="Wieland2011">{{cite book|last=Wieland|first=Terry |title=Gun Digest Book of Classic American Combat Rifles|date=November 22, 2011|publisher=Krause Publications|location=Iola, Wisconsin|isbn=978-1-4402-3017-2|page=100}}</ref> For these reasons, the US military declared this muzzle device a compensator, but it is more commonly known as the "GI", "A2", or "Birdcage" muzzle device.<ref name="Crawford2003">{{cite book|author=Steve Crawford|title=Twenty First Century Small Arms: The World's Great Infantry Weapons|url=https://books.google.com/books?id=z7nW8LpDOBoC&pg=PA85|access-date=May 28, 2013|year=2003|publisher=Zenith Imprint|isbn=978-0-7603-1503-3|pages=85–86}}</ref> The standard AR15 muzzle device conforms to the STANAG dimensional requirements for firing [[22 mm grenade|22 mm rifle grenades]].

===Magazines===
{{Unreferenced section|date=November 2024}}
The Colt AR-15 uses 20- or 30-round staggered-column [[STANAG magazine|detachable box magazines]]. Low-capacity 5- or 10-round magazines are also available to comply with legal restrictions, for [[hunting]], for benchrest shooting or where a larger magazine can be inconvenient.

=== Comparison to military versions ===
The primary distinction between civilian semi-automatic rifles and military models is [[select fire]]. Military rifles were produced with firing modes, [[Semi-automatic firearm|semi-automatic fire]] and either fully [[Automatic firearm|automatic fire]] mode or [[Burst mode (weapons)|burst fire]] mode, in which the rifle fires three rounds in succession when the trigger is depressed. Most components are interchangeable between semi-auto and select fire rifles including magazines, sights, upper receiver, barrels and accessories.<ref name=gundigest/><ref>{{cite book|last1=Zimba|first1=Jeff|title=The Evolution of the Black Rifle|date=2014|publisher=Prepper Press|isbn=978-0692317266}}</ref> The military [[M4 carbine]] typically uses a {{convert|14.5|in|adj=on}} barrel. Civilian rifles commonly have 16-inch or longer barrels to comply with the [[National Firearms Act]].<ref>{{cite book|last1=Muramatsu|first1=Kevin|title=Gun Digest Guide to Customizing Your AR-15|date=2014|publisher=F+W Media, Inc|isbn=978-1440242793}}</ref>

In order to prevent a civilian semi-automatic AR-15 from being readily converted for use with the select fire components, Colt changed a number of features. Parts changed include the lower receiver, bolt carrier, hammer, trigger, disconnector, and safety/mode selector. The semi-automatic bolt carrier has a longer lightening slot to prevent the bolt's engagement with an automatic sear. Due to a decrease in mass the buffer spring is heavier. On the select fire version, the hammer has an extra spur which interacts with the additional auto-sear that holds it back until the bolt carrier group is fully in battery, when automatic fire is selected.<ref>{{cite book|last1=Hanks|first1=D. A.|title=Workbench AR-15 Project|date=2004|publisher=Paladin Press|isbn=1610048466}}</ref> Using a portion of the select fire parts in a semi-automatic rifle will not enable a select fire option.<ref name="Leghorn">{{cite web|last1=Leghorn|first1=Nick|title=Ask Foghorn: What's the Difference Between a Full Auto and Semi-Auto Only AR-15 Bolt Carrier?|url=http://www.thetruthaboutguns.com/2012/06/foghorn/ask-foghorn-whats-difference-between-full-auto-semi-auto-only-ar-15-bolt-carrier/|website=The Truth About Guns|date=June 27, 2012|publisher=THETRUTHABOUTGUNS.COM|access-date=March 6, 2018|archiveurl=https://web.archive.org/web/20170711032652/http://www.thetruthaboutguns.com/2012/06/foghorn/ask-foghorn-whats-difference-between-full-auto-semi-auto-only-ar-15-bolt-carrier|archive-date=July 11, 2017}}</ref>{{Better source needed|date=October 2024}} As designed by Colt the pins supporting the semi-auto trigger and hammer in the lower receiver are larger than those used in the military rifle to prevent interchangeability between semi-automatic and select fire components.<ref>{{cite book|last1=Sweeney|first1=Patrick|title=Gunsmithing the Ar-15, the Bench Manual|date=2016|publisher=F+W Media, Inc|isbn=978-1440246609}}</ref>