AR-15 vs. M16: How Two Legendary Rifles Evolved & Differ

Few rifles have left as indelible a mark in the world of firearms as the AR-15 and M16. These two iconic weapons, born from the same lineage, have shaped the landscape of civilian and military shooting for decades. 

These firearms have taken divergent paths—one becoming a beloved civilian sporting rifle, the other a battle-tested military weapon that has seen action worldwide. But what sets these seemingly similar rifles apart?

The AR-15’s Military Potential

The story of the M16 begins with the AR-15, a lightweight rifle designed by Eugene Stoner at ArmaLite in the 1950s.

Originally chambered for the .223 Remington cartridge, the AR-15 caught the eye of the U.S. military, which was seeking a more compact and versatile rifle to replace the M14. Colt acquired the rights to the AR-15, and with a few modifications, the M16 was born. 

Adopted by the U.S. Air Force in 1964 and the Army in 1967, the M16 became the standard-issue rifle for American forces during the Vietnam War. (ref)

Overcoming Early Challenges

The M16’s journey was not without its challenges. Early models suffered from reliability issues due to inadequate maintenance and using a different powder in the ammunition, leading to frequent jamming in combat conditions. 

However, subsequent improvements, such as adding a forward assist and chrome-lined barrel in the M16A1 variant, helped mitigate these problems. These enhancements solidified the M16’s place as a reliable and effective combat rifle.

From Military to Civilian Market

While the M16 was making its mark on the battlefield, the AR-15 continued to evolve in the civilian market. Colt began selling semi-automatic rifle versions to the public in 1963, and the AR-15 quickly gained popularity among sport shooters and hunters. (ref)

This transition from military to civilian use marked the beginning of the AR-15’s journey as a separate entity from its military counterpart.

The Rise of Customization

As the patent for the AR-15 expired, other manufacturers began producing their own versions, leading to a wide array of customization options and accessories. 

Today, the term “AR-15” is used to describe a vast family of semi-automatic rifles based on the original ArmaLite design. These rifles have variations in barrel length, caliber, and furniture to suit different needs and preferences. 

This modularity has become one of the AR-15’s most defining features, allowing users to tailor their rifles to specific applications.

Firing Modes & Legal Distinctions

Despite their shared lineage, the AR-15 and M16 have key technical differences.

The most significant distinction lies in their firing modes. The AR-15 is typically semi-automatic, meaning it fires one round per trigger pull, while the M16 has select-fire capabilities, allowing for semi-automatic, burst, or fully automatic fire. 

This difference is technical and legal, as fully automatic weapons are heavily regulated in the civilian market.

Barrel Specifications & Performance

Other differences include barrel length and twist rate. The M16 features a 20-inch barrel with a 1:7 twist rate, optimized for the heavier 5.56x45mm NATO rounds. At the same time, AR-15s often have shorter barrels (16 inches being the most common) with varying twist rates depending on the intended use. 

These variations in barrel specifications can affect factors such as muzzle velocity, accuracy at different ranges, and the rifles’ overall handling characteristics.

The M16’s Military Legacy

The AR-15 and M16 have left an indelible mark on the world of firearms. The M16 has served as the U.S. military’s primary rifle for over half a century, seeing action in conflicts from Vietnam to the present day. (ref)

Its design has influenced the development of countless other military rifles worldwide, cementing its place in military history and doctrine.

The AR-15’s Civilian Impact

Meanwhile, the AR-15 has become a staple in the civilian market, cherished by enthusiasts for its modularity, accuracy, and versatility. (ref) Its popularity has spawned an entire aftermarket parts and accessories industry, allowing users to customize their rifles to suit their specific needs. 

The AR-15’s widespread adoption has also sparked ongoing debates about gun rights and regulations, further highlighting its significant impact on American culture and politics.