M4A1

The M4A1 is a carbine in the AR-15/M16 family chambered for 5.56×45mm NATO. It is a shorter, lighter variant of the M16 rifle designed for close-quarters combat and vehicle operations. The M4A1 incorporates a 14.5-inch barrel and a gas-operated, direct impingement system. Its flat-top upper receiver supports optical sights and other accessories via a Picatinny rail, and it generally uses a detachable box magazine (commonly 30 rounds). The weapon is equipped with a telescoping stock for length adjustment and quick adjustment in varied combat environments. An underbarrel grenade launcher (such as the M203) is optional on many configurations.

Fire control is selective-fire, enabling semi-automatic and fully automatic fire; some configurations historically offered a three-round burst as well. The M4A1 is designed for compatibility with standard 5.56×45mm NATO ammunition and with a wide range of accessories, optics, grips, and fore-end attachments.

Operational history and usage: The M4A1 was developed in the United States in the late 20th century and has become a standard issue carbine for many U.S. military branches, including the Army, Marine Corps, and special operations forces, as well as numerous allied forces. It has seen extensive service in conflicts such as those in Afghanistan and Iraq, and it remains in widespread use, often alongside newer variants and modernization programs.

Manufacturers and variants: Originally produced by Colt Defense, the M4A1 concept has since been manufactured by multiple vendors under license or agreement, with variations such as the M4A1 SOPMOD Block II introduced to improve optics, rails, and accessories. The M4A1 remains closely related to the M4 Carbine and the broader M16 family.