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Smart Bombs: Military, Defense and National Security

What Made the M16 Such a Great Rifle

M16 Rifle (M16A2 Version)
M16 Rifle (M16A2 Version). Image: Creative Commons.

Though the M16 rifle had a rocky start, it addressed a crucial need in the United States military: a fully automatic rifle that was both lightweight and controllable.


After the conclusion of the Second World War, drawbacks to the iconic M1 Garand design became apparent. Though the rifle benefitted from the powerful .30-06 cartridge, it was hindered by its low 8-round capacity and could fire in semi-automatic only. Though the rifle also served on the Korean Peninsula, its shortcomings were affirmed.

What the United States needed was a new, fully-automatic rifle.

M16 Rifle Variations.

M16 Rifle Variations.

A New Solution

The idea of an automatic rifle paired with an intermediate cartridge was first pioneered on a large scale by Nazi Germany during the waning days of the Second World War. Many of Germany’s dying gasps were technological flops, though their Sturmgewehr 44 (German for “Assault Rifle 44”) represented nothing less than a revolution in firearms design. The rifle was chambered in the intermediate 7.92×33mm Kurz cartridge and combined the high rate of fire of a submachine gun with the stopping power of a rifle and the compactness of a carbine. 

Though an attempt was made via the M14 to put a full-powered, fully-automatic rifle into the hand of soldiers and Marines, the design was inadequate. Rather than an intermediate-power cartridge, the M14 was chambered in the now NATO-standard 7.62x51mm cartridge, which was much too powerful for fully-automatic firing — necessitating yet another redesign after just five years of service.

Enter the M16

The M16 was based on the AR-15 rifle, now a ubiquitous American rifle chambered in the intermediate .223 Remington cartridge. Like the StG 44, the M16 brought a high rate of fire and lightweight profile onto a magazine-fed platform. The M16 rifle weighed less than the heavy, wooden-stock M14 and was much more controllable during automatic fire. Its advantages were immediately obvious.

M16 Training

Two JGSDF soldiers conducting weapons familiarization training with M16A4 rifles

Despite the M16 superior characteristics, there were however several drawbacks that became apparent — and deadly — after its Vietnam combat debut.


Jams and other malfunctions were a common complaint that contributed to solder’s perception of the M16 as an unreliable rifle. Another complaint was the M16’s lack of stopping power compared to the M14’s larger 7.62x51mm cartridge, especially when shooting through the dense jungle foliage endemic to Vietnam, which caused bullets to lose velocity and stopping power.

Eventually, reliability issues were addressed by improved soldier instruction on how to clean and maintain their M16 rifles, and by a better distribution of cleaning kits. After these and other design improvements were incorporated into the M16 design, confidence in the rifle increased.


Since its introduction, the M16 has spawned a number of copies, variants, and derivative rifles in both the United States and abroad, though has largely been supplanted by the very similar, though more compact M4, essentially a carbine version of the M16. Another rifle visually similar, though mechanically different than the M16 has recently been adopted by the United States Marine Corps, the M27 rifle — and coincidentally the rifle that was used to shoot Osama bin Laden.

Still, the M16 rifle filled an important capability gap when introduced into service in the 1960s in Vietnam.

Caleb Larson is a Defense Writer based in Europe. He holds a Master of Public Policy and covers U.S. and Russian security, European defense issues, and German politics and culture.

Written By

Caleb Larson, a defense journalist based in Europe and holds a Master of Public Policy degree from the Willy Brandt School of Public Policy. He lives in Berlin and writes on U.S. and Russian foreign and defense policy, German politics and culture.



  1. Ed Timperlake

    January 7, 2021 at 4:54 pm


    As a Quantico trained Marine infantry officer in 1969 the M-16 was considered a total Vietnam War dangerous POS weapon.

    It jammed in firefights because numerous design flaws included machining tolerances that allowed little amounts of dirt, mud, dust et al to jam it quickly.

    The M-14 simply shrugged such amounts and kept firing as being a reliable and very powerful infantry weapon in very nasty conditions.

    The round was also dangerous because the ejector would often strip the rear off living a partially expended round in the chamber with the next one up taking home and jamming the breech

    Smart platoon leaders had what was known as their “ram-rod” fireteam member (1 Marine out of four) to use his bore cleaning ramroad clear the jam.

    My M-14 never ever failed on fully auto- and when I transitioned to M-16 it always jammed

    Everything was eventually fixed but a courageous friend in an M-16 v AK-47 fire right told his Marines to grab AKs from the dead NVA- the problem was the distinct noise an AK makes- if not life or death he could have been facing a courtmartial

    Blaming the troops in not keeping their M-16 clean is a real insult to a poorly initially designed weapon.
    Semper Fi

    • Chris

      January 8, 2021 at 9:43 am


      I would second Ed’s comments regarding not blaming the troops. At the time the M-16 was introduced, the United States was behind the Soviets in the automatic weapons race. The US Military spent the time after WWII focusing on other priorities. The Soviets realized the power of the Sturmgewehr 44, and thus were already developing a similar weapon during WWII. They spent years developing, testing, and refining a weapon that would be easy to manufacture, and would be able to operate in any condition where the Soviet troops could be deployed.

      By the time the US realized it was behind, they were already in the beginning stages of the Vietnam conflict. Robert McNamara had to find a solution, and fast. The following is from a memorandum he wrote to Cyrus Vance in 1962.

      “… which appears to indicate that: 1. With the M-14 rifle in 1962, we are equipping our forces with a weapon definitely inferior in firepower and combat effectiveness to the assault rifle with which the Soviets have equipped their own and their satellite forces worldwide since 1950.”

      The M-16 also had a requirement from the United States Infantry Board, that any infantry rifle should be able to penetrate a steel helmet at 500 yards. The M-16 was originally developed using a powder known as IMR 4475. But in 1962, the Army allowed Colt to use another powder, WC 846. WC 846 lowered the pressure in the chamber, and increased the muzzle velocity of the projectile, thus improving the rifle’s accuracy and penetrating power at long distances. The new powder was dirtier than the IMR 4475. Since the M-16 vents into the bolt carrier, cleanliness of the powder is instrumental in its ability to fire.

      Additionally, the weapons initially lacked adequate corrosion resistance. Robert Fremont, who was initially an ArmaLite employee, joined Colt to help identify and address the problem. In his report to Colt’s President in 1966, he stated that “Colt’s weapons are sadly lacking in corrosion resistance”. Colt had apparently neglected this step in the manufacturing process.

      The Army also apparently did not supply the troops with adequate cleaning supplies. Lieutenant Colonel Herbert P. Underwood visited troops in Vietnam to try and identify why there were issues with the M-16. The following is from his report from 1966.

      “The 173rd uses some field expedience, primarily for cleaning the chamber and the bore of the weapons. They either use a piece of common wire, a shoe lace or a nylon cord which they carry with them. They take a 30 caliber patch cut it in half, fold it once and loop the string or what ever it is to the center of this patch. Then using oil they pull it through the bore of the weapon starting from the chamber. As they do this, they clean both the chamber and the bore and then dry it off. They also put a little bit of oil on it. I have not been able to find anyone that does not put a little bit of oil in the chamber of the weapon to prevent it from corroding. I try to discourage it, however I am not completely convinced myself that if you leave the chamber completely dry you won’t have a problem resulting from corrosion, even if you cleaned your weapon every day.”

      The jungle is not very forgiving to metal, especially when it is not protected or clean.

      The “soldier’s did not know how to clean their weapons”, was an excuse. The sad truth is that our soldiers, in Vietnam, were fighting with a prototype. The NVA were fighting with a proven, tested, and reliable weapon.


  2. Mario

    January 15, 2021 at 9:56 am

    It was recognized that to make a full auto rifle controllable the caliber had to be below 7mm. The Euro armies were developing 6.8 mm rifles to do the job and thought we were crazy for going to a puny 5.56mm. Our NATO Allies went to 5.56 because they would be dependent on the US for ammo resupply in the event of a war in Europe. When the AR-15 (not the M-16) was fielded to the Army, it was billed as a self cleaning weapon so it was not fielded with a weapons cleaning kit. The barrels were deliberately not chromed by the Army to save money which resulted in corrosion (rusting)in the chamber and the barrel itself. The dirty powder was used because Dupont had many tons of cannon powder that it wanted to unload so they talked the army into allowing them to regrind it so it could be used in the 5.56 rifle rounds. Between the filth from the fired ammo and the corroded chambers the rifle jammed frequently. The army could have copied the piston system of the AK or the M-1 but they chose a gas operation system and it resulted in a lot of Soldiers/Marines needlessly being killed.

    When the Army finally did something about the problems (chromed the barrel, bigger gas tube, and a new bolt carrier group with serrations for the Forward Assist)they redesignated the rifle as M-16A1. The pencil thin barrel is still a problem for the rifle while use in sustained or full automatic fire as the barrel warps.

    Additionally, the military also failed to fix another major problem, Buffer Tilt, which makes the rifle barrel climb uncontrollably when fired in 3 round bursts and full auto. Its a cheap fix but they have refused to do it.

    BTW When I went through basic training at FT Know in the Summer of 76 my rifles lower was stamped AR-15 and not M-16A1


    No 60 years later we are going to a 6.8 caliber weapon with a piston system.

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