Colt AR-15 .223/5.56 Semi-automatic Rifle

AR-15

The AR-15 comes in many sizes and has many options,

depending on the manufacturer. The part shown bottom

center is the lower receiver with pistol grip and trigger

assembly. Under U.S. law the lower receiver alone is the

component legally considered the "firearm".

TypeSemi-automatic rifle /

service rifle

Place of origin United States

Service history

In service 1958–present

Production history

DesignerEugene Stoner, Jim

Sullivan, Bob Fremont

Designed 1957

Manufacturer

ArmaLite, Colt,

Bushmaster, Rock River

Arms, Stag Arms, DPMS

Panther Arms, Olympic

Arms, and others.

Specifications

Weight

2.27 kg–3.9 kg (5.5–

8.5 lb)

Barrel length

24 in (610mm)

20 in (508 mm)

standard

18 in (457 mm)

16 in (406 mm)

14.5 in (368 mm)

11.5 in (292 mm)

7 in (178 mm)

6.5 in (165mm)

Cartridge .223 Remington, 5.56

NATO, 300 Whisper,

7.62x35mm, .22 long

rifle

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 firing range

400–600 m (avg 547 yd)

[5][6]

Feed system

Various STANAG

magazines. 20, 30, 50

STANAG

Sights

Adjustable front and rear

iron sights

Modified AR-15

Description

The AR-15 is a lightweight, intermediate cartridge magazine-fed, air-cooled rifle with a rotating

lock bolt, actuated by direct impingement gas operation or long/short stroke piston operation. It

has been produced in many different versions, including numerous semi-automatic and selective

fire variants. It is manufactured with extensive use of aluminum alloys and synthetic materials.

The AR-15 was first built by ArmaLite as a small arms rifle for the United States armed forces.

Because of financial problems, ArmaLite sold the AR-15 design to Colt. After modifications

(most notably the relocation of the charging handle from under the carrying handle like the AR-

10 to the rear of the receiver), the new redesigned rifle was subsequently adopted as the M16

rifle.[7] Colt then started selling the semi-automatic version of the M16 rifle as the Colt AR-15 for

civilian sales in 1963 and the term has been used to refer to semiautomatic-only versions of the

rifle since then.[8] Although the name "AR-15" remains a Colt registered trademark, variants of

the firearm are independently made, modified and sold under various names by multiple

manufacturers.

As of 2012, there are an estimated 2.5-3.7 million rifles from the AR-15 family in civilian use in

the United States.[42] They are favored for target shooting, hunting, and personal protection, and

have become the most popular rifle in America.

History

The AR-15 is based on the 7.62 mm AR-10, designed by Eugene Stoner, Robert Fremont, and L.

James Sullivan of the Fairchild Armalite corporation.[9] The AR-15 was developed as a lighter,

5.56 mm version of the AR-10. The "AR" in all ArmaLite pattern firearms simply stands for

ArmaLite, and can be found on most of the company's firearms: AR-5 a .22 caliber rifle, the AR-

7, another .22 caliber, the AR-17 shotgun, the AR-10 rifle, in addition to the AR-24 pistol.

1973 Colt AR-15 SP1 rifle with 'slab side' lower receiver (lacking raised boss around magazine

release button) and original Colt 20 round box magazine

ArmaLite sold its rights to the AR-10 and AR-15 to Colt in 1959. After a tour by Colt of the Far

East, the first sale of AR-15s was made to Malaya on September 30, 1959, with Colt's

manufacture of their first 300 AR-15s in December 1959.[10] 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. 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. Later heavy-barrel versions of the civilian AR-15 can weigh upwards of 8.5 lb.[11]

Today the AR-15 and its variations are manufactured by many companies and are popular among

civilian shooters and law enforcement forces around the world due to their accuracy and

modularity (for more history on the development and evolution of the AR-15 and derivatives see

M16 rifle).

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 referred to by

the term AR-15.

Some notable features of the AR-15 include:

Aircraft grade forged 7075-T6 aluminum receiver is lightweight, highly corrosion-

resistant, and machinable.

Modular design allows the use of numerous accessories such as after-market sights,

vertical forward grips, lighting systems, night vision devices, laser-targeting devices,

muzzle brakes/flash hiders, sound suppressors, bipods, etc., and makes repair easier.

Straight-line stock design eliminates the fulcrum created by traditional bent stocks,

reducing muzzle climb.

Small caliber, accurate, lightweight, high-velocity round (.223/5.56x45mm)

Easily adapted to fire numerous other rounds.

Front sight adjustable for elevation.

Rear sight adjustable for windage (most models) and elevation (some models).

Wide array of optical aiming devices available in addition to or as replacements of iron

sights.

Direct impingement gas system (as designed) with short or long stroke gas piston, or

direct blowback operating systems available.

Synthetic pistol grip and butt stock that do not swell or splinter (regulated in some states).

Various magazine capacity, ranging from 10 to 30-round or more.

Ergonomic design that makes the charging handle, selector switch (which also engages

the safety), magazine release, and bolt catch assembly easy to access.

4 MOA Accuracy as a MILSPEC standard.

AR-15 sight picture

Semi-automatic AR-15s for sale to civilians are internally different from the full automatic M16,

although nearly identical in external 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 to

satisfy United States Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) requirements

that civilian weapons may not be easily convertible to full-automatic. In the late 1970s and early

1980s, items such as the "Drop In Auto Sear" or "lightning-link," conversion to full automatic

was very straightforward (sometimes requiring machining of the lower receiver with use of a

mill and M16 Bolt Carrier Group).[12][13] Such modifications, unless using registered and

transferable parts made prior to May 19, 1986, are illegal. (The Firearm Owners Protection Act

in 1986 has redefined a machine gun to include individual components where a semi-automatic

firearm can be converted to full-automatic based on a 1981 ATF ruling on machine gun parts.)

Since 1993, The Bolt Carrier Groups used in AR-15 type rifles for civilians have employed

additional measures to prevent modification to full auto. Colt AR-15's use a metal alloy wall

separating the Fire Control group from the Sear, preventing use of such items.

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 Colt AR-15 models do not have three-round burst or automatic

settings; they can only be fired as a semi-automatic, and are therefore not selective fire weapons.

In semi-automatic-only variants, the switch only functions to rotate between safe and fire. Some

other manufacturers may mark their rifles with three-positions for collectors and re-enactors,

though the guns will not fire in those modes. However weapons modified to full automatic using

a lightning-link are capable of full automatic fire only—unless a special full automatic fire select

mechanism and modified selector-switch is substituted.[12]

Operating mechanism

Diagram of an M16 rifle, firing

The main 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 a short distance in line with the stock of the rifle to

first unlock the bolt. 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. (The gas

system only serves to unlock the bolt once the projectile has exited the barrel). 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. The bolt is much heavier than the projectile, and along with the recoil-

spring pressure inside the stock buffer-tube performs the cartridge ejection function and

chambers the following cartridge.

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, .300 Blackout, .45 ACP, 5.7x28mm, 6.5 mm Grendel, 6.8 mm

Remington SPC,[14] .50 Beowulf, .50 BMG, and .458 SOCOM.[15] It is not recommended to

chamber the 5.56x45 NATO into a rifle designated .223 Remington, due to the increased

chamber pressure in the 5.56mm cartridges; the two cartridges are similar, but not

identical.

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

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 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. The 9mm cartridge fires from an unlocked breech, or straight

blow-back—rather than a locked breech, because the spring and bolt provide enough weight to

allow this type of functioning. These guns do not utilize the direct gas impingement method of

operation like the original.

5.56×45mm NATO compared to .50 Beowulf cartridges.

Some AR-15's like the POF, LWRCI, H&K, Sturm Ruger, Sig Sauer, CMMG, and Adams Arms

offerings replace the DGI (direct gas impingement) operating system with a short stroke/long

stroke gas piston system. These guns usually have modified bolt carriers, gas keys, and gas

blocks. When fired, DGI systems dump high pressure hot gas through the gas tube to the bolt

carrier key and into the bolt carrier group. This can rapidly heat up the bolt carrier group and

cause excessive fouling, one of the main complaints about the design. Gas piston operating

systems alleviate these problems, but can be the cause of other issues such as carrier tilt, which

can lead to increased bolt fractures.

Some manufacturers offer upper and lower receivers machined from a solid billet (block) of

aluminum as opposed to an aluminum forging. Forgings typically having a comparatively higher

strength to weight ratio than billet.

Upper receivers utilizing a monolithic rail system that combine a railed hand guard and upper

receiver into one uninterrupted piece are made by companies like Colt's Manufacturing

Company, Lewis Machine and Tool (LMT MRP), POF-USA, and VLTOR. This is done to

provide a continuous uninterrupted rail section that runs along the top of the gun from the

weapon's charging handle to the front sight/gas block. This rail section is used for the mounting

of sights, laser aiming devices, night vision devices, and lighting systems.

A side charging upper receiver has been developed by LAR Grizzly. Blackwood Arms has also

developed a side charging upper receiver.[16] The charging handle can be had in a left side, right

side, or ambidextrous configuration. Since the charging handle is attached to the bolt carrier

making it a reciprocating design, it can be utilized as a forward assist device as well.

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, longer projectiles tend to perform better with faster rifling rates. [17]

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 for 7.62x39mm, 1:9 for the 6.5 Grendel and 1:8 for

.300 Blackout.

A Colt AR-15 on display at the National Firearms Museum. This example is fitted with an early

waffle-patterned 20-round magazine.

Standard issue magazines are 20- or 30-round staggered-column magazines, traditional box

magazines 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 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. Surefire is now offering

extended capacity magazines in 60- and 100-round capacity configurations. These are of a

staggered column design, dubbed casket magazines due to their shape.

Muzzle devices

Most AR15 rifles have a barrel threaded in 1⁄2-28" threads to incorporate the use of a muzzle

device such as a flash suppressor, sound suppressor or muzzle brake.[18] The initial design 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 and 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.[19] For these reasons, the US Military declared this muzzle device a

compensator; but it is more commonly known as the "GI" or "A2" flash suppressor.[20]

Some jurisdictions have banned or severely restrict usage of flash suppressors by law. In most of

these areas, AR-15 shooters have installed muzzle brakes or compensators on their rifles.

The threaded barrel allows sound suppressors with the same thread pattern to be installed directly

to the barrel; however this can result in complications such as being unable to remove the

suppressor from the barrel.[21] A number of suppressor manufacturers have turned to designing

"direct-connect" sound suppressors which can be installed over an existing flash suppressor as

opposed to using the barrel's threads.[21]

Malfunction

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 the external

dimensions of the two cases are the same and 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 .

Internally the 5.56x45mm case wall is thicker, and the round itself is typically loaded to produce

higher pressure than the .223. 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.[45]

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 of Greenup, IL, 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 many

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.[46] Another type of malfunction, hammer follow, is also a potential problem for AR

platform weapons.

AR-15 and variant manufacturers

U.S.

Alexander Arms

American Spirit Arms

ArmaLite

Barrett Firearms Manufacturing

Bushmaster Firearms International

Charles Daly firearms

Colt's Manufacturing Company

DPMS Panther Arms

Daniel Defense

FNH USA

High Standard Manufacturing Company

Knight's Armament Company

Les Baer

Lewis Machine and Tool Company

Land Warfare Resources Corporation International (LWRCI)

Magpul Industries

Olympic Arms

Para-Ordnance (Para-USA)

Remington Arms

Rock River Arms

Ruger

Sabre Defence /Manroy USA

Sig Sauer

Smith & Wesson

Stag Arms

Sturm, Ruger

Wilson Combat

Z-M Weapons

International

Colt Canada (previously Diemaco)

Ferfrans

Heckler & Koch

Norinco

Sig Sauer

United Defense Manufacturing Corporation

Schmeisser

Oberland Arms (Germany)

HERA Arms (Germany) Dynamic Arms Research DAR (Germany)

Calibers

Pistol cartridges

Metric

FN 5.7×28mm

7.62×25mm Tokarev

9×19mm Parabellum

9x21

10mm Auto

Imperial

.357 SIG

.40 S&W

.400 Corbon

.41 Action Express

.45 GAP

.45 Super

.45 ACP

.45 Winchester Magnum

.50 Action Express

Rifle cartridges

Metric

5.45×39mm

5.56×45mm NATO

6mm TCU

6×45mm

6×47mm

6mm PPC

6mm Whisper

6mm WOA

6mm Hagar

6mm BR Remington

6×45mm

6.5mm Whisper

6.5mm Grendel

6.5mm PPC

6.5 WSSM

6.5 WOA

6.8 mm Remington SPC

7mm Whisper

7mm TCU

7.62×39mm

Imperial

.177

.17 Practical

.17 Remington

.17-223

.17 HMR

.17 HM2

.204 Ruger

.20 Tactical

.20 Practical

.20 VarTarg

.221 Fireball

.22 LR

.22 WMR

.222 Remington

.222 Remington Magnum

.223 Remington

.223 Remington Ackley Improved

223 WSSM

243 WSSM

.25 Winchester Super Short Magnum

.25×45mm

.30 Remington AR

.300 Whisper

.30 Herrett Rimless Tactical

300 AAC Blackout (7.62×35mm)

.30 RAR

.300 OSSM

.30 Carbine

.35 Gremlin

.358 WSSM

.450 Bushmaster

.458 SOCOM

.50 Beowulf

Shotgun shells

.410 bore

In addition, the AR-15 lower receiver can be used as a trigger mechanism for single shot or side-

fed upper receiver platforms that shoot in a variety of larger calibers, including .50 BMG and

crossbow bolts.