What’s the Difference Between an AR15, M4, and M16?

What’s the Difference Between an AR15, M4, and M16?

Over the past 20 years, the AR-15 has become the most popular rifle in America. It displays an excellent combination of reliability, accuracy, ergonomics, and modularity that have stood the test of time. But what exactly is an AR-15? Is it a brand? A style of rifle? Due to the heavy media coverage of the AR-15 over the past couple of decades, there’s a lot of misunderstanding and confusion over what exactly constitutes an AR-15 versus an M16 versus an M4.

In this article, we will cover the fundamental differences so you can understand the characteristics of each type of rifle.

What does AR-15 stand for, and what is an AR-15?

There are two main definitions for AR-15, and both are technically correct. The original meaning of the AR in AR-15 was ArmaLite Rifle since ArmaLite was the company that developed the new rifle system in 1956 based on its larger-caliber AR-10 rifle. The numerical designations were sequential at the time, and the firearm designs were wildly different. (ArmaLite also produced the AR-1, AR-3, AR-5, AR-7, AR-9, AR-11, etc.) However, due to the eventual widespread adoption of the original AR-15/M16 rifle platform by America and its allies (more on this below) and the huge commercial popularity of the semi-automatic, commercial, civilian version of the rifle, the term AR-15 today encompasses an entire world of rifles and carbines, very few of which are visually similar to the original ArmaLite rifle.

AR-15 Rifle With Bipod, Optic, and Magazine Inserted

Today, AR-15 refers to a vast family of semi-automatic rifles and carbines based on the original ArmaLite rifle or the Colt commercial AR-15 variant of the 1970s and 1980s. However, there is no longer a standard AR-15 barrel length, buttstock configuration, handguard, or optic/rail/iron sight setup. Due to the platform's commercial success, hundreds of companies now making AR-15s in nearly any barrel length or style you can dream up. Any semi-automatic rifle patterned after the ArmaLite/Colt design style can correctly be termed an AR-15. Or, if you want to be pedantic, an AR-15 style rifle.

A brief history of the AR-15

The original ArmaLite AR-15 was developed by Jim Sullivan as an adaptation of Eugene Stoner’s larger AR-10. In the mid-1950s, the AR-10 (in caliber 7.62x51 NATO) was proposed and evaluated as a potential new service rifle for the US military to replace the outdated M1 Garand. Several countries selected the AR-10 as a new service rifle, but for political reasons, the US military went with the M14 (closely related to the M1 Garand).

Early reports of the M14 in combat showed that it was nearly uncontrollable in full-auto fire. It was also extremely heavy (around 10 pounds loaded) compared to the ArmaLite and other designs (under 7 pounds), and the .30 caliber ammunition was also very heavy. This limited the number of rounds each soldier could carry. The primary alternative of the day was the M1 Carbine (and its full-auto-capable M2 variant), which was very light and compact. Still, the .30 Carbine ammunition didn’t provide satisfactory ballistics or wounding capability for a main-issue rifle. Several military big-wigs proposed a new, lighter rifle firing a high-speed, lightweight, ballistically effective cartridge. As a result, in 1957, Jim Sullivan of ArmaLite was tasked with scaling down the AR-10 to accommodate the new 5.56x45mm round, based on the commercial .222 Remington cartridge.

Jim Sullivan at Inchon Harbor, Korea in 1954

Image: Jim Sullivan at Inchon Harbor, Korea in 1954. Image courtest of Small Arms Review.

The resulting AR-15 was extremely light, weighing just over 6.5 lbs with a loaded 20-round magazine. The AR-15 was first put into service with the ARVN (Army of the Republic of Viet Nam) and small experimental squads around 1958. The muzzle velocity of the new .22 caliber bullet was well over 3,000 feet per second (fps) upon exiting the 20-inch barrel, and this speed was the key to the new cartridge’s effectiveness on enemy combatants. The bullet would tumble and fragment when entering soft tissue, and despite being a full-metal-jacketed (FMJ) projectile, it produced devastating and effective wounds.

Reports from combat were favorable, and the rifle was proving reliable. Military studies on the experimental squads that had been armed with AR-15s compared to M14s showed that a 5-7 man team carrying AR-15s had equivalent firepower to an 11-man team armed with M14s. Troops could also carry three times more AR-15 ammunition compared to the larger, heavier M14 ammo and magazines. The AR-15 was found to be three times more reliable than the M14 rifle. Despite this performance, the M14 was selected as the US Army’s new service rifle in 1959.

Armed Forces Man Shooting M14

Image courtest of Military Today.

Due to this frustrating situation, as well as financial difficulties and limitations in manpower and production capacity, ArmaLite sold the rights to its AR-15 design to Colt. Colt made a few modifications (such as changing the charging handle position from the top to the rear of the receiver) and started manufacturing in 1959. Colt marketed the rifle to multiple military and civilian security services worldwide. It was known as the Colt ArmaLite AR-15 Model 01, and later, Colt renamed it the 601.

The AR-15 developed enough fans that in July 1960, General LeMay, Vice Chief of Staff of the US Air Force, ordered 8,500 rifles and decreed the AR-15 to be the new Air Force standard service rifle. The Army was still evaluating the AR-15 compared to the M14. Still, the results from the field were so overwhelmingly in favor of the new, lighter rifle that it was adopted in 1962 and officially designated the M16 service rifle in December 1963, entering full production in 1964.

General LeMay Shooting Trap

General LeMay Shooting Trap. Image courtesy of Smith & Wesson Forum.

While also making the M16 for the US armed forces, Colt continued using the AR-15 trademark for its semi-automatic-only rifles marketed to civilian and law-enforcement customers, known as the Colt AR-15.

Until the 1990s and early 2000s, AR-15s weren’t really a thing in the American shooting culture. The Colt AR-15 was two to three times as expensive as other, similarly capable rifles of the time, and other than a few veterans or other in-the-know customers, not many people bought them. Not many people liked the black, angular appearance. However, the 1994 Clinton gun ban increased people’s awareness of the rifle, and more manufacturers began making their own versions of the AR-15. (Colt’s patent expired in 1977.) As more and more people became aware of the excellent attributes of the rifle and aftermarket support grew, the popularity of the AR-15 platform exploded.

Today, there are over 500 companies manufacturing AR-15s and many more offering parts and accessories. The AR-15 is so easy to customize and modify to a user’s specific tastes that it’s sometimes jokingly referred to as LEGO for grownups.

Video: Basic Disassembly of the AR-15

What’s the difference between an AR-15 and an M16?

Sixty years ago, the answer would have been nothing. As mentioned above, the original Colt/ArmaLite AR-15 was a select-fire (fully automatic) rifle, and the AR-15 was adopted in 1962-1963 and became the M16. The first M16s widely issued to US troops in Vietnam were marked COLT AR-15 on the receiver. Most of the early soldiers in Vietnam called their rifles AR-15s.

M16 rifle

The M16 has a 20-inch barrel and a fixed buttstock and has been updated over the years as the:

  • M16A1 (1967: added a forward bolt assist by request of the US Army, chrome-plated bore, revised flash hider, fencing around magazine release)
  • M16A2 (1983: changed from fully automatic to 3-round burst select-fire, added shell deflector, heavier/faster-twist barrel, round handguards, finger-groove grip, longer buttstock, revised bolt assist button, revised rear sight adjustment mechanism)
  • M16A3 (1994: rare Navy/special forces variant of the M16A2 with full-auto capability)
  • M16A4 (1997: removable carry handle, Picatinny rail on the receiver)

However, the AR-15 is now primarily known as the commercial, semi-automatic platform of rifles made in the original style. So, it can be correctly stated that the M16 is a select-fire military service rifle, while the AR-15 is now any member of the family of semi-automatic, commercial rifles adapted from the original design.

Video: M16 Full Auto Suppressed

Due to its length and fixed buttstock, the M16 has somewhat fallen out of favor in most military organizations. It is generally replaced by the M4 or, eventually, by the NGSW (Next-Generation Squad Weapons) XM5 or XM7.

What’s the difference between an M16 and an M4?

In the most basic terms, an M4 is a shorter, handier version of the M16 service rifle. The M4 is considered a carbine—pronounced CAR-bean (rhymes with the word seen) or CAR-byne (rhymes with the word line). A carbine is traditionally a lighter, shorter version of a longer rifle. The M4 has a 14.5-inch barrel compared to the M16’s 20-inch barrel. The M4 has a collapsable, adjustable buttstock compared to the M16’s fixed buttstock. The M4 has a carbine-length gas system compared to the M16’s rifle-length gas system. Most modern M4s are full-auto, while most M16s use a 3-round burst mechanism.

M4 Carbine Rifle

Why and when was the M4 developed?

The spiritual ancestors of today’s M4 carbine were the Vietnam-era CAR-15, XM177, and GAU-5A family, which were experimental or limited-issue carbines (they were called submachine guns at the time) based on the M16, with very short barrels and collapsible buttstocks. Due to the intense muzzle blast from their 10 to 11.5-inch barrels, these firearms were usually fitted with sound moderators or suppressors to help prevent hearing damage and reduce flash signature.

Popular with Special Forces and other elite units, these were specialized weapons and weren’t widely issued or adopted across the US military.

However, the concept and benefits of a shorter, potentially lighter version of the M16A2 continued to circulate. In 1983, the US military asked Colt (making most of the US’s M16 rifles) to design a shorter M16 carbine. Colt began work on a new carbine design called the XM4 (X for experimental), taking some of the best features of the XM177E2, Colt’s commercial carbines, and the most recent M16A2 rifle.

Video: The M4 Carbine: Aged to Perfection

The XM4 was ready for testing by mid-1985. There were multiple variants during the next few years of testing and evaluations. Some had A1-style sights; some had A2-type sights. Some had 14.5-inch barrels with provisions for a bayonet lug and M203 grenade launcher, and some didn’t. Various barrel twist rates were tried. The shell deflector was incorporated into the upper receiver. By May 1991, the XM4 was renamed the M4, and Colt provided a manual for the new carbine, which was issued in limited numbers to specialized squads. In 1994, the M4 entered general service, first seeing action in Kosovo in 1999. By 2005, the M4 had begun replacing the M16 in most units.

The M4 has semi-automatic and three-round burst firing modes (like the M16A2 and M16A4), while the M4A1 has semi-automatic and fully automatic firing modes (like the M16A1 and M16A3).

As far as weight, a fully-kitted battle-ready M4 can often weigh nine or even 10 pounds, so it can’t be considered lightweight. However, its collapsible buttstock and shorter barrel (compared to the M16) are highly favored by soldiers who frequently have to ride in vehicles or engage in CQB (Close Quarters Battle) situations.

So, to sum up, in the simplest terms, the M16 platform is the rifle-length select-fire assault rifle used by the US military and many NATO allies, based on the original AR-15 ArmaLite assault rifle. The M4 platform is a shorter, carbine-length assault rifle based on the M16 and is currently the standard weapon for most US military service branches and squadrons, though the M16 platform is still in limited use. The AR-15, as it stands today, is the civilian or commercial platform encompassing all semi-automatic variants of this design, whether in rifle or carbine-length configuration.

Store your AR-15's and other firearms in a Liberty Safe

Whether you have one AR-15 or a whole bunch, remember to keep all your guns safe from theft, fire, and unauthorized access in a US-made Liberty safe. Multiple sizes, configurations, styles, and prices are available to fit anyone’s taste and budget. Look through our online gun safe catalog, or visit a Liberty Safe showroom near you.


*Made in the U.S.A. from U.S. and Global Parts.


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