Type: Assault Rifle
Caliber: 5.56x45mm NATO
Capacity: (5, 20, 30, 40 round box magazine/ 90 round snail drum/ 100 round dual drum Beta-C magazine (STANAG Magazines)
Fire Modes: Safe/Semi (Mk 12 SPR, AR-15, civilian variants) Safe/Semi/Burst (M16A2, M16A4, M4) Safe/Semi/Auto (M16, M16A1, M16A3, M4A
Colt M4A1EditThe M4 Carbine is a 14.5" barreled select fire Assault Rifle. It has a distinctive 'step down' in the barrel to allow for mounting the M203 grenade launcher. Many of them in the battlefield are customized with forearm rails (usually holding the AN/PEQ-2 IR designator, a vertical forward grip, sometimes a flashlight, or one of many types of rifle scopes and red-dot or reflex optics). The M4 has three round burst capability, while the M4A1 has full auto fire capability. The very earliest M4s delivered to the U.S. Army had fixed carry handles and were known in Colt's catalog as the Model 777; however, soon after, the military started buying the Model 920, which featured a detachable carry handle, but continued to call these guns "M4s". Contrary to popular misconception, the carry handles on most M4s and M4A1s are detachable, and most of these carbines are used with the carry handle removed, and a folding rear sight and optic being attached to the receiver instead. As far as the procurement program has always been concerned, the burst/auto capability is the only difference between an M4 and M4A1, however, more recently produced M4A1s also have a thicker barrel profile under the handguards along with a heavier buffer to slow the rate of fire, meaning that the weapon is more controllable during fully automatic firing and is less prone to overheating.
What is confusing is that many civilian commercial makers of AR-15 style rifles call their 16" Carbine "The M4". Though there is no rule saying they can't name their gun whatever they want, the official M4 is the version used and originally issued by the U.S. Army and built by Colt. Colt tried to sue other gun makers to stop using the term 'M4' however, it was ruled that M4 refers to a type of firearm and Colt cannot copyright the term.