M16 rifle

[20] The M16A1 incorporated numerous modifications including a bolt-assist ("forward-assist"), chrome-plated bore, protective reinforcement around the magazine release, and revised flash hider.

[49] The 5.56 mm round had to penetrate a standard U.S. helmet at 500 yards (460 meters) and retain a velocity over the speed of sound while matching or exceeding the wounding ability of the .30 carbine cartridge.

After testing the AR-15 with the ammunition manufactured by Remington that Armalite and Colt recommended, the Air Force declared that the AR-15 was its 'standard model' and ordered 8,500 rifles and 8.5 million rounds.

[27] Advocates for the AR-15 in the Defense Advanced Research Projects Agency acquired 1,000 Air Force AR-15s and shipped them to be tested by the Army of the Republic of Vietnam (ARVN).

[27] At this point, the bureaucratic battle lines were well-defined, with the Army ordnance agencies opposed to the AR-15 and the Air Force and civilian leadership of the Defense Department in favor.

However, General Maxwell D. Taylor, chairman of the Joint Chiefs of Staff, advised President John F. Kennedy that having two different calibers within the military system at the same time would be problematic and the request was rejected.

[66] United States Army Special Forces personnel filed battlefield reports lavishly praising the AR-15 and the stopping power of the 5.56 mm cartridge, and pressed for its adoption.

While the Olin WC 846 powder achieved the desired 3,300 ft (1,000 m) per second muzzle velocity, it produced much more fouling, which quickly jammed the M16's action (unless the rifle was cleaned well and often).

However, the rifle was initially delivered without adequate cleaning kits[44] or instructions because advertising from Colt asserted that the M16's materials made the weapon require little maintenance, leading to a misconception that it was capable of self-cleaning.

[44][77] Documented accounts of dead U.S. troops found next to disassembled rifles eventually led to a Congressional investigation:[78] We left with 72 men in our platoon and came back with 19.

Because the bolt is prevented from moving forward by the barrel, the carrier is driven to the rear by the expanding gases and thus converts the energy of the gas to the movement of the rifle's parts.

This accumulating carbon and vaporized metal build-up within the receiver and bolt carrier negatively affects reliability and necessitates more intensive maintenance on the part of the individual soldier.

"[59] In March 1970, the "President's Blue Ribbon Defense Panel" concluded that the issuance of the M16 saved the lives of 20,000 U.S. servicemen during the Vietnam War, who would have otherwise died had the M14 remained in service.

[95] Another underlying cause of the M16's jamming problem was identified by ordnance staff that discovered that Stoner and ammunition manufacturers had initially tested the AR-15 using DuPont IMR8208M extruded (stick) powder.

Requests included greater bullet lethality, newly built instead of rebuilt rifles, better-quality magazines, decreased weight, and a collapsible stock.

Later M16 models and the M16A1 had an improved rifling with six grooves, right-hand twist, one turn in 12 inches (1:304.8 mm or 54.8 calibers) for increased accuracy and was optimized to adequately stabilize the M193 ball and M196 tracer bullets.

M16A2 and current models are optimized for firing the heavier NATO SS109 ball and long L110 tracer bullets and have six grooves, right-hand twist, one turn in 7 in (1:177.8 mm or 32 calibers).

The unmarked approximately 0.070 in (1.78 mm) diameter aperture rear sight is for normal firing situations, zeroing and with the elevation knob for target distances up to 800 meters.

[128][note 6] "In Fallujah, Iraq Marines with ACOG-equipped M16A4s created a stir by taking so many headshots that until the wounds were closely examined, some observers thought the insurgents had been executed.

[140] The 5.56×45mm NATO cartridge can also produce massive wounding effects when the bullet impacts at high speed and yaws ("tumbles") in tissue leading to fragmentation and rapid transfer of energy.

[157] This upgrade is designed to maximize performance of the 5.56×45mm round, to extend range, improve accuracy, increase penetration and to consistently fragment in soft-tissue when fired from not only standard length M16s, but also the short-barreled M4 carbines.

[182] Draft Standardization Agreement 4179 (STANAG 4179) was proposed to allow NATO members to easily share rifle ammunition and magazines down to the individual soldier level.

However, once established, the use of the system was expanded to other accessories, such as tactical lights, laser aiming modules, night vision devices, reflex sights, foregrips, bipods, and bayonets.

The new buttstock was lengthened by 5⁄8 in (15.9 mm) and included a fully textured polymer buttplate for better grip on the shoulder and retained a panel for accessing a small compartment inside the stock, often used for storing a basic cleaning kit.

When inspecting some using a borescope, they discovered that a burr left from drilling/reaming the gas port was causing copper fouling to build up at the front sight block, interfering with the gauge used.

Colt also produces M16A4 models for international purchases: A study of significant changes to Marine M16A4 rifles released in February 2015 outlined several new features that could be added from inexpensive and available components.

Those features included: a muzzle compensator in place of the flash suppressor to manage recoil and allow for faster follow-on shots, though at the cost of noise and flash signature and potential overpressure in close quarters; a heavier and/or free-floating barrel to increase accuracy from 4.5 MOA (Minute(s) Of Angle) to potentially 2 MOA; changing the reticle on the Rifle Combat Optic from chevron-shaped to a semi-circular reticle with a dot at the center used in the M27 IAR's Squad Day Optic so as not to obscure the target at long distance; using a trigger group with a more consistent pull force, even a reconsideration of the burst capability; and the addition of ambidextrous charging handles and bolt catch releases for easier use with left-handed shooters.

Officially adopted as a replacement for the M3 "Grease Gun" (and the Beretta M9 and M16A2 for select troops) in 1994, it was used with great success in the Balkans and in more recent conflicts, including the Afghanistan and Iraq theaters.

Other M5 variants and calibers are the: M5 SCW (Sub-compact weapon) (5.56×45mm); M5 300 (.300 AAC Blackout); M5 SMG (9×19mm); CMK (7.62×39mm); M7 Battle Rifle (7.62×51mm) and Designated Marksman and Semi-Automatic Sniper System (both 5.56×45mm).

Diemaco changed the trapdoor in the buttstock to make it easier to access and a spacer of 0.5 inches (13 mm) is available to adjust stock length to user preference, along with the addition of hammer-forged barrels.

From top to bottom: M16A1 , M16A2 , M4A1 , M16A4 .
A Marine of the 3rd Battalion, 1st Marines cleans his XM16E1 in December 1967.
The M16 gas redirect system, incorrectly labeled as direct impingement. The gif does not show the operating mechanism of the rifle, only the gas redirect system.
Front cover – The M16A1 Rifle – Operation and Preventive Maintenance by Will Eisner , issued to American soldiers in the Vietnam War .
Video of Rifle 5.56mm, XM16E1, Operation and Cycle of Functioning
M16 internal piston action system
M16 sight picture when using the 0.070 in (1.78 mm) rear aperture
M16A2 with unmarked aperture rear sight for normal firing situations raised. The larger aperture, marked '0-2', is flipped down.
Fully adjustable rear sight, brass deflector and forward assist of the M16A2
NATO E-type silhouette target
Vietnam War-era 20-round magazine (left) and current issue NATO STANAG 30-round magazine (right)
Improved tan colored M16 magazine follower
Loading an M203 40 mm grenade launcher attached to an M16A1 rifle with a practice round.
M234 riot control launcher
An early M16 rifle without forward-assist. Note: "duckbill" flash suppressor and triangular handguard.
M16A1 rifle with 30-round magazine
Spent case being deflected after firing an M16A2 (Model 705 with Safe/Semi/Burst trigger group) by a left-handed user.
M16A2 Enhanced rifle (Model 708 with Safe/Semi/Burst/Auto trigger group)
M16A2 with a heat shield hand guard and an M203 grenade launcher under it
M16A3 with a Safe/Semi/Auto trigger group
M16A4 rifle with a removable carrying handle, polymer handguards and M7 bayonet mounted
M16A4 rifle with ACOG sight, railed hand guard and foregrip
A USAF Combat Control Team member with a GAU-5 carbine and oversized flash suppressor
An M4A1 carbine (foreground) and two M16A2s (background) being fired by U.S. Marines during a live fire exercise : though adopted in the 1990s and derived from the M16A2, the M4 carbine was part of a long line of short-barreled AR-15 used in the U.S. military
M5 carbine
A Canadian soldier fires the current issue C7A2 rifle at the range with a C79 A2 sight. This particular example is missing the standard TRIAD mount.
US Navy Mk 12 Special Purpose Rifle
M231 FPW
Worldwide users of the M16
Current
Former
Afghan National Army soldiers with M16A2 rifles.
Canadian soldiers patrol Kandahar Afghanistan armed with C7 (M16 type) rifles.
Malaysian Army soldier with an M16A1 equipped with an M203 grenade launcher during a CARAT Malaysia 2008.
Soldiers of the Israel Defense Forces in training with M16A1 rifles with the A2 style handguard.
Philippine marines using M16A1 rifles with the A2 style handguard during a military exercise.
South Korean soldiers toss bayonet mounted M16 rifles into the air at the celebration ceremony for the 65th Anniversary of the South Korean armed forces.
Vietnamese Army (ARVN) Rangers armed with M16s defend Saigon during the Tet Offensive.
United States Marine firing an M16A4 equipped with an ACOG .
Indonesian soldiers accompanying the Heritage Flag Hoisting Troops are seen holding M16A1 and SS1 rifles while marching.
Palestinian Security Forces with an M16A1 & M16A2 rifles during exercise in Gaza, 2012.