Firearm model names and designations can be confusing at times. Many gun enthusiasts use “AR-15” and “M16” interchangeably in many contexts, and if you’re unaware of the differences between the two, it may seem nonsensical.
Why use different terms if they’re the same? Are they the same at all? Learn the differences between the AR-15, the M16, and the history behind each designation.
The Origin of the AR-15 Designation
In 1956, three engineers at ArmaLite, then a division of the Fairchild Corporation, began developing a revolutionary new type of rifle: a Small-Caliber, High-Velocity (SCHV) rifle, based on the requests and specifications of General Wyman of the U.S. Continental Army Command (CONARC).
The three engineers working on this project were Eugene Stoner, Jim Sullivan, and Bob Fremont. Based on ArmaLite’s earlier 7.62mm AR-10, this new weapon was the ArmaLite AR-15, a .223-caliber light rifle.
At that point, the AR-15 designation meant ArmaLite Rifle 15, one of many small arms designs the company had produced.
All products designed by the original ArmaLite company between 1954 and 1983 followed the same “AR-x” nomenclature, starting with the AR-1 Parasniper, a prototype bolt-action rifle, and ending with the AR-18 and its civilian variant, the AR-180.
How the AR-15 Became the M16
Due to financial difficulties, ArmaLite had no choice but to sell their AR-15 and AR-10 designs to Colt’s Manufacturing Company in 1959.
Colt proceeded to make changes and alterations to the original AR-15 rifle, renaming it in the process. It received a new commercial designation: “Colt ArmaLite AR-15 Model 01,” and internally referred to as the Colt Model 601.
One of the most notable changes was the charging handle’s location: Colt moved it from under the carrying handle to behind it, where it remained ever since.
By 1960, the Colt AR-15 made its way into U.S. Air Force service, marking the AR-15’s official entrance into U.S. service. However, the rifle did not see service with any other branches of the U.S. military until 1963, when Secretary of Defense Robert McNamara ordered its adoption by the Army.
Following minor modifications, Colt produced a second version of the AR-15. Internally known as the Colt Model 602, it received its full U.S. Army designation: Rifle, Caliber 5.56mm, M16, later simply referred to as the M16, starting a long line of military rifles and carbines.
The Dichotomy Between Military and Civilian Rifles
Shortly after the U.S. Army officially adopted the M16, Colt discontinued the original Colt ArmaLite AR-15 (Colt Model 601) and started producing a semi-automatic-only version for the civilian market.
This new rifle became known as the Colt AR-15 SP-1 Sporter (internal code: Colt Model R6000), with the first units hitting the market in 1964.
Civilian shooters begin differentiating the two models in common parlance. The classic AR-15 vs. M16 dichotomy is born.
In the minds of most gun enthusiasts, the AR-15 is the civilian rifle. The M16 is the military weapon.
In 1977, Eugene Stoner’s patent on the Stoner direct impingement gas system expired, allowing manufacturers other than Colt to produce firearms using the same action.
Although Colt retains partial control of the term “AR-15” in the form of a registered trademark to this day, it only prevents other gun manufacturers from calling their rifles “AR-15.”
The American gun community started referring to rifles modeled after the original Colt AR-15 under various monikers, such as “AR-15 style rifles,” “AR-15 family,” “AR-15 platform,” or simply, if confusingly, “AR-15s.”
The AR-15: A Type of Rifle?
Over time, despite Colt’s continued ownership of the AR-15 trademark, the vast majority of gun owners today consider “AR-15” to refer to a family of firearms.
The Colt AR-15, the Colt M16, and modern incarnations of these rifles all share the same Stoner-style direct impingement gas system used in the original ArmaLite AR-15. Consequently, all of these rifles may be correctly called “AR-15s.”
The only practical difference between these rifles on a mechanical level is whether the weapon can fire in fully automatic mode (or burst mode).
Rifles with full-auto or burst mode capability are almost always military weapons, legally classified as machine guns by the ATF under the National Firearms Act of 1934. Although technically legal, possession of these rifles is heavily restricted and unattainable to the average citizen.
However, certain firearms have very similar looks and ergonomics to an AR-15; yet, they are mechanically very different. For example, although the Heckler & Koch HK416 looks similar to a modern AR-15 carbine, it uses a short-stroke gas piston mechanism instead of the original Stoner DI action.
Despite the identical controls and manual of arms, the HK416 is mechanically far closer to firearms such as the AR-18 than the AR-15. Other commonly-seen examples are pistol-caliber carbines employing the distinctive features and ergonomics of an AR-15, even featuring partial compatibility with standard AR-15 parts.
Despite the appearances, such firearms usually function using the relatively simple straight blowback action, far removed from the gas-operated system of the original .223 rifle.
Although most agree on the original AR-15 vs. M16 dichotomy created in 1964s, the question of whether to call non-direct impingement rifles “AR-15s” continue to spark heated debates within gun-owning communities.
Some argue for a stricter definition, excluding any rifle not using the Stoner DI system, no matter how visually or ergonomically similar. Others recognize that rifles using the AR-15’s controls and ergonomics is more than a matter of internal mechanisms, arguing that shooters may need a term with a looser, more inclusive definition.
In an attempt to respond to these debates, the National Shooting Sports Foundation coined the term Modern Sporting Rifle (MSR) in 2009, explicitly referencing the confusion surrounding the “AR” and “AR-15” designations.
In the NSSF’s view, an MSR is a civilian-owned, semi-automatic rifle with modern features, including but not limited to firearms that look like, or are derived from, military rifles. This definition draws a clear distinction between the firearms intended for civilian usage and weapons meant for military service (i.e., assault rifles).
Throughout the years AR-15 has evolved from rifles to pistols to legally adapt to state laws pertaining to firearms, understand the difference of AR-15 rifles from pistols on this comprehensive comparison guide.
The Breakdown
If you need a single, definitive answer to the question, look at it this way: An M16 is part of the AR-15 family. But an AR-15 is not necessarily an M16.
They are not strictly the same, but they are related.
Most shooters today generally understand that “M16” and related military designations (such as “M4”) refer strictly to military firearms, usually not accessible to civilians.
Therefore, in the vast majority of contexts, the term AR-15 refers to a semi-automatic rifle, usually but not always employing the original ArmaLite AR-15’s mechanism, or at the very least possessing controls and ergonomic features identical to an AR-15s.
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