AR15, M4, M16: Decoding the Differences

Eric Sof

What's the difference between an AR15, M4, and M16?

The distinction between an AR-15, M4, and M16 is a common inquiry. To provide a clear and concise response, the AR-15 is a semi-automatic civilian version of the M16 rifle. The M4, on the other hand, is a shorter and more compact version of the M16, often used by the military in close-quarters combat. M4 and M16 are fully-automatic firearms, meaning they can fire multiple rounds with a single trigger pull. The AR-15, being semi-automatic, can only fire one round per trigger pull. It is important to note that certain states and countries may have different regulations regarding the ownership and use of these firearms.


The AR-15, also known as the ArmaLite Rifle, is a derivative of the previous model, the AR-10. It is a selective-fire, 5.56x45mm caliber, an air-cooled, gas-operated, magazine-fed rifle with a rotating bolt and straight-line recoil design. Eugene Stoner designed the rifle to create a lightweight assault rifle that could fire a new, high-velocity, small-caliber cartridge. In 1959, the license to produce the AR-15 was acquired by Colt, who continued to manufacture the rifle under the brand name Colt ArmaLite AR-15.

AR-15 semi-automatic rifle
What’s the difference between an AR15, M4, and M16: AR-15 semi-automatic rifle (Photo: Creative Commons)

After some modifications, the AR-15 was adopted by the United States Army as the M16. However, Colt did not discontinue the AR-15 brand and today; it can be found as semi-automatic modern sporting rifles primarily used for recreational shooting and are made for civilians.


The M16 rifle, officially known as the Rifle, Caliber 5.56 mm, M16, is a modified version of the Armalite AR-15 rifle adopted by the United States military. The initial M16 design featured selective-fire capabilities, firing the 5.56x45mm cartridge with a 20-round magazine capacity. The M4 carbine, a newer iteration, was derived from the M16 with the intent of creating a shorter and more compact model while still retaining many of the features of the M16, including firing capabilities and the 5.56x45mm cartridge but with a shorter barrel and less weight.

M16A2 US soldier on shooting range
What’s the difference between an AR15, M4, and M16: U.S. soldier shooting from M16A2 assault rifle (Photo: XY)


The M4 carbine, a newer model of the M16 rifle, was designed to be a shorter and more compact version while retaining many of the M16’s features. It is a 5.56x45mm NATO caliber, air-cooled, direct impingement gas-operated, magazine-fed weapon with a 14.5-inch barrel and a telescoping stock.

The M4 carbine is widely utilized by the United States Armed Forces, particularly as a primary infantry weapon in the United States Army and United States Marine Corps, replacing the M16 rifle in many combat units. It’s capable of firing in semi-automatic and three-round burst modes, with a slightly more advanced version called the M4A1, which can be fired in semi-automatic and fully-automatic modes.

An M4A1 rifle with upgraded SOPMOD Block II kit
What’s the difference between an AR15, M4, and M16: An M4A1 rifle with upgraded SOPMOD Block II kit (Photo: XY)

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1 thought on “AR15, M4, M16: Decoding the Differences”

  1. How do I get a stamp and permit and how much is the costs?

    If acquired, how would I convert my weapon to fully?

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