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U.S. M16

The M16 stands as a symbol of American military history from the Cold War to the present.


U.S. Army photos

The door gunners began to fire bursts with their M60 machine guns as the helicopters dropped into the clearing. To the left of the flight, a mountain known as the Chu Pong Massif rose 1,500 feet above the valley floor. At its base, a dry creek bed and dense jungle bordered a clearing code-named landing zone X-Ray. The force conducting the combat assault was the 1st Battalion, 7th Cavalry Regiment under the command of 42-year-old Lt. Col. Harold “Hal” Moore. As the Huey’s skids touched the LZ, Lt. Col. Moore yelled “Let’s go!” to his men and took-off running for the edge of the clearing, firing his rifle as he ran. It was Nov. 14, 1965, and it was the beginning of one of the most dramatic engagements of the war in Vietnam—the Battle of Ia Drang Valley.

North Vietnamese soldiers and Viet Cong guerillas fought the battle armed with either the SKS or the AK-47. The Americans were armed with the XM16E1—a revolutionary new select-fire rifle often referred to simply as the “Black Rifle.” In his After Action Report for the battle of LZ X-Ray, Lt. Col. Moore had nothing but praise for the rifle he and his men carried into the Ia Drang Valley: “Brave soldiers and the M16 brought this victory.” He even referred to it as “the best individual infantry weapon ever made, clearly the answer to the enemy’s AK-47.” It was an auspicious beginning for a rifle that differed so significantly from the ones that came before it. First of all, it was lightweight mainly because of the use of aircraft-grade aluminum and plastic in its construction. Secondly, whereas previous generations of infantry rifles fired the powerful .30-’06 Sprg. or 7.62x51 mm NATO cartridges, the XM16E1 was chambered in the M193 5.56 mm cartridge (also known as .223 Rem.)—a small-caliber, high-velocity cartridge that was thought to be better suited for modern, close-range combat environments. The 55-grain bullets reached a muzzle velocity of 3,250 fps and tended to tumble after striking a target. In fact, an early promotional pamphlet for the rifle stated, “on impact the tumbling action of the .223 caliber ammunition increases effectiveness.” This “effectiveness” had actually been demonstrated in Vietnam long before the 7th Cavalry got there.

In 1958, the ArmaLite Division of Fairchild Aircraft Corp. introduced the first prototype of its .22-cal. version of its select-fire AR10 rifle that it called the AR-15 (the “AR” stood for ArmaLite Rifle). Weighing barely more than 7 pounds with a loaded 20-round magazine and easily controllable in fully automatic, the AR-15 seemed like the perfect arm for the small-statured soldiers of the Army of the Republic of Vietnam (ARVN) who were fighting-off a growing communist insurgency. That being the case, a full-scale test of the AR-15 was conducted during the first half of 1962 using 1,000 new Model 01 rifles. They were distributed among several ARVN units and American advisors and carried into the field to be used against the Viet Cong. The comments that came back from the American advisors were “extremely favorable” of the AR-15 and the lethality of the .223 cartridge. One report related an encounter between ARVN Rangers and three Viet Cong in heavy jungle on June 16, 1962. One of the rangers fired a burst from his AR-15 at one of the VC, hitting him with three rounds at a range of only 15 meters: “one round in the head took it completely off—another in the right arm, took it completely off, too—one round hit him in the right side, causing a hole about five inches in diameter.”

Although lurid, such accounts of the unforgiving effectiveness of the AR-15 and the .223 cartridge exerted convincing influence on the American military. Soon after the tests in South Vietnam, the U.S. Air Force officially adopted the rifle followed by the U.S. Navy, which ordered a small number of rifles to arm its SEAL teams. But the remarkable lethality of the high-velocity .22-cal. bullet was about to change. The Model 01 AR-15s that were used for the test had 20-inch barrels with rifling that made one complete twist in 14 inches (1:14 inches). That rate provided adequate accuracy but imparted the marginal gyroscopic stability on the bullet that permitted tumbling on impact. Continued testing by the U.S. Air Force determined that, because of the 1:14-inch rifling, the AR-15 Model 01 did not group as well in dense arctic air. The AR-15’s rifling was therefore changed to one twist in 12 inches, which imparted greater stability to the bullet but may have resulted in a reduction in its lethality.

Despite being described as “the best individual infantry weapon ever made” in 1965, the XM16E1 began to exhibit catastrophic problems in 1966. Reports from the field indicated that U.S. troops in Vietnam were experiencing chronic failures to extract. In the malfunctions, a cartridge’s brass case would seize fast in the chamber and the extractor would tear through the rim. Such a stoppage could only be cleared by pounding the case out of the chamber from the muzzle end using a cleaning rod—something that was terribly impractical and dangerous to do in the middle of a firefight. This situation was exacerbated by the fact that XM16E1s were not issued with cleaning rods at this stage in production. In fact, they even lacked compartments for cleaning kits in the buttstocks. When a cleaning rod could even be scrounged at all, troops resorted to taping them to the forward handguards of their rifles. Through the end of 1966 and into 1967 these malfunctions reached chronic levels and resulted in lives lost on the battlefield. After one especially violent battle, a Marine wrote home to his mother saying “Before we left Okinawa, we were all issued this new rifle, the M16 … practically every one of our dead was found with his rifle torn down next to him where he had been trying to fix it.”

On Feb. 28, 1967, the XM16E1 was standardized as the M16A1 rifle at the height of the jamming epidemic when troop confidence in the rifle had reached an all-time low. Amid widespread rumors, word of the problems endemic to the M16A1 soon reached U.S. Congressional leaders. In May, the House Armed Services Committee of the 90th Congress established the Special Subcommittee on the M16 Rifle with Representative Richard Ichord (D-Mo.) as chairman. The three-member “Ichord Committee” immediately went to work during the summer of 1967 investigating the causes of the malfunctions. Although the military attempted to blame the malfunctions on improper cleaning and maintenance, the committee quickly determined that the root cause was ammunition—specifically, gunpowder. When the 5.56 mm M193 round was first adopted by the military in September 1963, only DuPont’s IMR 4475 nitrocellulose gunpowder was approved for loading it. As a result of a series of technical challenges that manufacturing the new round presented, a fateful decision was made on April 28, 1964, to allow M193 ammunition to be loaded with Olin Mathieson’s WC 846 ball powder. A double-base nitrocellulose/nitroglycerine propellant, the ball powder exerted higher chamber and gas port pressures and also left behind carbon fouling. The higher gas port pressure resulted in increased cyclic rate—a problem initially resolved after the introduction of a modified recoil buffer. But high port pressure, high chamber pressure and carbon corrosion were ultimately to blame for the outbreak of XM16E1 extraction failures in Vietnam.

When the Ichord Committee submitted its 51-page final report in October, it recommended the withdrawal of Olin Mathieson’s WC 846 ball powder and the immediate introduction of chrome chambers on all production rifles. Thus, at about the same time as the Tet Offensive in early 1968, the often-tragic field malfunctions experienced with the XM16E1 began to fade away. Soon thereafter, production at Colt’s was supplemented when contracts to produce the M16A1 were awarded to the Hydramatic Division of General Motors in Ypsilanti, Mich., and Harrington & Richardson, Inc. of Worcester, Mass. Completed rifles from these three manufacturers armed U.S. units during the Nixon years of the war in Vietnam. From the violent battles in the A Shau Valley in 1969 to the incursion into Cambodia during the summer of 1970, the rifle proved itself a highly effective infantry weapon. Even after the withdrawal of front line U.S. forces began in 1971, the M16 remained in Vietnam until the bitter end: XM16E1s and M16A1s armed U.S. personnel during the evacuation of the U.S. embassy in Saigon on April 30, 1975.

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8 Responses to U.S. M16

9th Div Bear wrote:
November 16, 2014

5.56 and .223 are the same thing!!!

David J Phillips wrote:
January 25, 2014

Hey Troy, FYI- not sure where you got your data, but I was issued one of those XM16E1's in the Corps in March of 1976 and yes sir, it was old as hell with a three prong flash hider as well. Mine wasn't being used as a test bed, it was my service issue weapon. I had the same type issued when I went to the 3rd Mar Div FMF PAC, so perhaps you are talking about other branches of the service who actually had money? If you will recall, Carter & co. pretty much gutted the military back then and each branch was 'scarfing up' anything they could to stay in the game.

Jeff wrote:
October 14, 2012

What's kept this weapon in service for so long is that it can be continually upgraded to newer versions and tweaked to fullfill a variety of mission requirements. The carbine version is already standard issue with the Army as of 2010 because it is the most user friendly with regards to fitting a variety of different sized soldiers and a variety of different missions like I mentioned, but the 62 grain bullet is only giving the weapon .22 hornet ballistics out of the shorter barrels, so a 77 grain bullet is being fielded to give the carbine the best ballistics possible. Excellent evolution over 5 1/2 decades.

Troy S. Lindstrand wrote:
September 25, 2012

there are errors in this story,It was not the XM16E1 that was the problem, but the M16. XM16E1 was the test bed for some of the imptovements that became the M16A1.Issued to S.F. and Airborne units in Vietnam.This information was also misinformed on the TV show.Served with both the M16A1 and M16A2 rifles,building ARs for 20 years and an historian. Thanks

tehbob wrote:
September 08, 2012

It is 5.56. M16s are not issued in .223. At least not a single one iv touched or heard about during my career.

sgtcowboyusmc wrote:
September 01, 2012

I believe this article is full of errors from the twist of the M16 to Caliber the M16 was issued in. The Author says the M16 was issued in .223 caliber until 1983. I was in the Corps from 1977-1984 and I never seen a .223 M16. All M16's I was issued had 5.56mm on them. Also when the Miltary adopted the M193 round it was designated the 5.56mm not .223. I would be interested if the author would e mail me and explain where he got his information as it is vastly different that I recall from being there!

mc wrote:
July 03, 2012

M16a2 had 1:7 twist rate, not 1:9. American rifleman should know better.

Frank wrote:
July 02, 2012

Having had the M14 and similar during my service time, it's still difficult to accept a .22 as a service rifle. My wife lays claim to a 5.56 rifle as she's not interested in the heavier recoil of the M1A/M14 or my Garand and that's fine - I'd rather she be able to hit her target consistantly. Mine is a 7.62X39 uppered version firing either 130 or 150 grain reloads. It's not that I've got any particular love for the Tinkertoys, but the ammo is cheap and plentiful.