The Evolution of the AR-15/M-16 Platform

We tend to look at the current M-4 series as being “new”, but just how long has the M-16 and its variants been around? The answer is, longer than some people realize. Let’s delve into the history of this platform.

Origins — Replacing the M-1 Garand

Way back in 1956, the US Army was testing various rifles to replace the M-1 Garand. The T44E4 and T44E5 (versions of the M-14) were entered into testing. Fabrique Nationale entered the T-48 (also known as the FN FAL). Armalite submitted their AR-10.

M1 Garand
It all started with a quest to replace the M-1 Garand.
The ArmaLite AR-10 partook in the trials to select a new service rifle for the US Military. It featured many innovative features, including a straight-line stock and barrel.

The AR-10 had some innovative features, including a straight-line stock/barrel design, phenolic composite furniture, a flash suppressor, and adjustable gas system. The upper and lower receiver were attached via takedown pins and the charging handle was located within the carry handle on top of the receiver. It weighed only 6.85 pounds. The caliber was the new 7.62x51mm and it was fed from a 20-round box magazine.

In the end, the Army chose the T-44, which was then designated the M-14. One supposes this choice may have been because so many service members were already familiar with the similar M-1 Garand at the time. Or maybe there were kickbacks. Who knows, at this point?

M-1A Scout Squad Rifle.
After winning the trials, the T44 was selected. It was then designated the M-14. Here is a modern example from Springfield Armory—the M-1A Scout Squad rifle. It’s similar to an M-14, but with a shortened, 18-inch barrel.

Troubles With the M-14

It wasn’t long before issues (perceived or real) surfaced about the M-14, which made its debut in Vietnam. The rifle was heavy and troops could not carry a lot of ammunition for it compared to the AK-47 assault rifles that they were facing. This spurred the search for a new weapon for the troops.

Despite being too heavy, the M-14 was well-liked by those who carried it into battle. It proved to be a very reliable rifle, and the 7.62 round hit hard.

It was around this time that the Army also decided that a change in caliber might be in order. A smaller round so the troops could carry more ammunition.

Military Adoption of the AR-15

Eugene Stoner revealed the AR-15 in 1957. AR stands for ArmaLite. It was similar to the AR-10 but used a .22 caliber centerfire cartridge (the .223). It fired semi and fully automatic and had a 20-inch barrel. Although the Army ignored it at first, the Air Force decided to adopt it and ordered 8,000 units, along with 8.5 million rounds of ammunition.

Eventually, 1,000 test rifles were shipped to Vietnam and tested by the ARVN (Army of the Republic of Vietnam).

In 1963, the US Special Forces adopted the AR-15 as its standard weapon. Other units, including Airborne units and branches of the CIA also adopted the rifle.

An early M-16 being fired in Vietnam on full auto. Note the lack of forward assist.
A soldier fires an early M-16 on full auto in Vietnam. Note the lack of forward assist. (Photo: War History Online)

The AR-15 was being more widely adopted, and Army Ordnance was given permission to modify the design as needed. The first modification was a manual bolt closure (today we know it as the Forward Assist), used in the event that a round did not fully chamber. Eugene Stoner did not think a forward assist was necessary, but the Army thought it was important that the troops have something to shove a stubborn round into the chamber, even if it was not often necessary.


At this juncture, the rifle was adopted officially as the M-16. Made of lightweight materials and using lightweight ammunition, it allowed soldiers to carry more ammo into combat, which meant they could be effective for a longer period of time. Additionally, the lighter recoil impulse of the .223 caliber meant that full auto fire was more easily controllable than typical .30 caliber rifles. Troops appreciated the lighter-weight rifle, too.

Back in the mid-1990’s, I was at my agency’s academy for sniper training. We were in the armory and I noticed an early AR-15 (it might have been an M-16), with a serial number in the 500 range. It was a very early example and was full auto. What struck me was the incredibly light weight of the rifle! It literally felt like a “Mattel Toy,” which is a nickname given to the early rifles by the troops who used them. Sadly, I wasn’t able to get any range time with this example, but it was fun handling it and checking it out.

Early Troubles 

The Marines were the last to get the M-16, hanging onto their M-14s as long as they were able to.

It wasn’t long before issues cropped up with the M-16. Rampant reports of stoppages were coming in. To make a long story short, the propellant used in the early batches of ammunition was gumming up the actions.

My close friend, Wayne, who was in Vietnam (82nd Airborne) told me that they were informed that the rifles did not need cleaning, as they were “self-cleaning.” Well, we all know that no weapon cleans itself—if there was one such self-cleaning weapon, I’d be one of the first in line to buy it!

At any rate, Wayne tells me the M-16 was a disaster and he hated it. In fact, to this day, he staunchly refuses to even pick up an AR-15/M-16, he hates them that much. I can’t blame him; if I were using a weapon in combat and it jammed, I wouldn’t be keen on it either. Wayne is not the only one who remembers the dark years of the M16; many others do too.

To make a long story short, manufacturers switched the powder propellants, which went a long way toward helping the reliability. Cleaning kits were also issued (apparently, the rifle wasn’t as self-cleaning as initially thought) and troops were trained in how to properly clean and maintain the rifle. These measures helped to fix the issues. Unfortunately, the M-16 had already gained a poor reputation among the troops.


In 1969, the M16A1 officially replaced the M-14. A few upgrades made the M16A1 superior to the original M-16. Among them was the addition of a chrome-lined barrel, a forward assist, and new 30-round magazines. It was found that the M16A1 increased reliability in Vietnam. The fact that it was finally realized that the rifles were not self-cleaning helped a lot. Instructions were issued, as were cleaning kits, which allowed troops to properly care for their weapons.

Soldier firing M-16A1 in Vietnam
The M16A1 featured upgrades, including a forward assist, which made it more effective and reliable. (Photo: PewPewTactical)
The M16A1 also featured a chrome-lined barrel. New 30-round magazines were introduced, but were in such short supply that members of some units actually purchased them from the commercial market with their own funds. (Photo: Wikipedia)


This model of M-16, added in 1966, is known by a couple of names: The CAR-15 (Colt Automatic Rifle), or Colt Commando.

It’s a shortened version of the M-16, meant to be even lighter, more portable, and handier. Barrel lengths are, initially, 10.5 and later, 11.5 inches, with a very long flash suppressor attached to the end of the barrel (it was approximately five inches long).

Two SF members armed with CAR-15s.
The CAR-15 was popular with SF and Recon Teams in Vietnam. Those who carried it loved its light weight and compact length. (Photo: SOFREP)

In 1967, the barrel was lengthened to 11.5 inches. This cut down slightly on the muzzle flash and blast, and allowed the mounting of the Colt XM148 Grenade Launcher.

To make it even more compact, the buttstock is telescoping, so it could be collapsed. Even today, we see similar buttstocks on AR-15/M-16s. It was made from aluminum and could be adjusted to two positions.

Instead of the standard triangular handguards of the M-16, those of the CAR-15 are round.

Initially, the CAR-15 was popular with Special Forces and SEALs, among other special teams, in Vietnam. Unfortunately, because of the shortened gas system, it was generally not as reliable as the M16A1.

The US Air Force adopted a version of the Colt Commando, designating it the GAU-5/A.

Production of the CAR-15 ceased in 1970 due to US forces in Vietnam winding down.

M-16 Carbine

Early in the 1970s, Colt began designing a carbine with a 14.5-inch barrel. Because this new carbine had a longer barrel, it used a standard M-16 flash suppressor, which made it no longer than the CAR-15 with its 11.5-inch barrel. The model adopted by the US Military featured a forward assist and telescoping buttstock.

Initial versions needed work on the gas system because of unreliability issues.

Air Force GUU-5P
The Air Force GUU-5P carbine. (Photo: Wikipedia)

It was adopted by the US Air Force and designated as the GUU-5/P.


1983 saw yet another upgrade for the M-16 series, this time being designated the M16A2. Improvements included a heavier barrel toward the end, near the flash suppressor. The new flash suppressor featured a solid bottom so as not to kick up dust.

The entire rear sight assembly was revamped, being more easily adjustable than that of the M16A1. This was a definite improvement, as elevation adjustments were much easier with this sight.

The handguards were made round and featured reinforcements. The heat shields in the handguards helped to keep the heat from the barrel away from the shooter’s hands.

Soldier firing the M16A2.
The M16A2 offered major improvements over the older models. Accuracy and performance were enhanced. It was first adopted by the US Marine Corps. Note the adjustment on the rear sight. (Photo: Sandboxx.US)

The pistol grip was changed slightly, featuring a swell part way down the grip. The stock was also lengthened slightly and reinforced.

A shell deflector was added to the right side of the receiver, just behind the ejection port. This helped deflect shells a bit better for those who shoot left-handed; the empty casings didn’t hit the shooter in the face.

Rather than full automatic fire, a 3-round burst mechanism was installed. Of course, semi-automatic fire is still possible as well. The 3-round burst mechanism seemed to be a solution looking for a problem. It’s easy enough to fire short bursts with the M-16 series without a silly mechanism to limit firing. To make matters worse, the burst mechanism makes the trigger pull inconsistent, even in semi-auto mode.

The barrel’s twist rate was also changed to a 1:7 twist, which stabilized heavier bullets.

Speaking of heavier bullets, a new 62-grain round was developed for the M16A2. It was designated as the M855 and features a steel core, still in use today. The faster twist rate and heavier bullet add to longer range accuracy and it penetrates better too. The 55-grain M193 projectiles that were used in the M16A1 could also be used in the M16A2.

Overall, the added features really did improve the M-16, making it sturdier and more accurate than earlier models.

The US Marines was the first service to adopt the M16A2, with other branches following.


The M16A3 was given the trigger group of the M16A1, which allows fully automatic and semi-auto fire.

A removable carry handle was added, which could easily be removed so that optics could be added to the receiver. Aside from that, the M16A3 was not an extraordinary departure from the M16A2.


This rifle also features a removable carry handle with an M1913 rail on the top. A Knight’s Armament M5 RAS handguard rail system is also available. This allows the A4 to be a more modular weapons system, permitting the mounting of scopes, lasers, lights, and all manner of accessories. Of course, the M203 40mm grenade launcher can also be fitted on the M16A4.

The weight is 8.5 pounds with a loaded magazine. It comes standard with semi and 3-round burst modes, but models are available that allow fully automatic fire.

M4 Carbine

The M4 is now the standard issue carbine of most units in the US Military.

Soldier firing the M4 on full auto in Iraq.
The current M4 has plenty of real estate to bolt on various gear, including scopes, lasers, lights, and grenade launchers. Photo: Reuters.

The M4 weighs 6.36 pounds with a 14.5-inch barrel. The overall length, with the stock extended, is 33 inches. It has a collapsible stock and a removable carry handle. A 1913 rail is standard for attaching optics and such. The M203 grenade launcher can be added, given the stepped barrel of the M4.

M4A1 carbine.
The Colt M4A1 features a 14.5-inch barrel and is widely issued to US troops. Photo: The Bourne Directory.

There are programs planned to continue upgrading the M4 in the future.

Final Word

This article does not cover every single iteration of the M16 series, as they are numerous. Rather, we hit the high points.

The M16/AR-15 has been around since the 1950’s and is the longest-serving rifle in US history. From Vietnam to Iraq and Afghanistan. That’s quite a testament!

It’s gone through some large and small changes over these decades, and likely will experience some more in the future. Troops using it these days generally like it. The M4 is fairly reliable and handy, making it popular.

Looking at a Vietnam-era M-16 and comparing it to an M-4 of today is quite a shock. The M-4 often has a scope and/or red dot sight, lights, IR and visible lasers, vertical grips… and the list goes on. It seems like a new gadget comes out every month to mount on the platform.

AR-15 with scope.
These days, the civilian AR-15 is wildly popular. The accessory options are endless.

Our readers are likely to have extensive experience with this weapons system. Feel free to leave comments, good and bad, about the M16, we’d love to hear from you.

Jim Davis served in the PA Dept. of Corrections for 16 ½ years as a corrections officer in the State Correctional Institute at Graterford and later at SCI Phoenix. He served on the Corrections Emergency Response Team (CERT), several of those years as a sniper, and also the Fire Emergency Response Team (FERT). For 25 years, he was a professional instructor, teaching topics including Defensive Tactics, Riot Control and Tactical Operations, Immediate Responder, and cognitive programs as an adjunct instructor at the DOC Training Academy. He was then promoted to the title of corrections counselor, where he ran a caseload and facilitated cognitive therapy classes to inmates. His total service time was close to 29 years. He was involved in many violent encounters on duty, including incidents of fatalities. He is a dedicated Christian and attributes any skills that he has to the glory of God.

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