The M4 is a shorter and lighter variant of the M16 rifle, with 80 percent of its parts being interchangeable. The remaining 20 percent of parts which cannot be swapped include the buffer spring and buffer weight, barrel, and gas tube due to the shorter carbine length.
As with most carbines, the M4 is handy and more convenient to carry especially in urban environments when compared to the M16 which is 14cm longer. At ranges beyond 200m, the M4 does take a slight knock on its ballistic performance. This can however be improved by selecting the correct ammunition to account for the shorter barrel, faster twist rate and reduced muzzle velocity.
The M4’s manoeuvrability makes it ideal for use in vehicles and CQB (close quarters battle). Special Operations Units often prefer the M4 over the M16. An upgraded M16 is preferred when used as a sharpshooter or designated marksman rifle chambered in 5.56mm.
M4 Carbine M16 Rifle
Design Year 1988 1957
In Service 1994 to present 1963 to present
Weight (Loaded) 3.1Kg 4.0Kg
Barrel Length 14.5-inch 20-inch
Cartridge 5.56x45mm 5.56x45mm
Bullet Weight (Standard) 55 - 77grain 55 - 77grain
Muzzle Velocity 884m/s 948m/s
Max. Effective Range 500 - 550m 500 - 600m
M16 Rifle
M4 Carbine
Terminology
Assault Rifle - a fully automatic, selective fire rifle that uses an intermediate cartridge and a detachable box magazine. It must be an individual weapon, it must be capable of selective fire, it must have an intermediate cartridge, the ammunition must be fed from a detachable box magazine, and it must have an effective range of 300m or more.
Carbine - a long arm firearm but with a shorter barrel than a rifle. Many carbines are shortened versions of full length rifles, shooting the same ammunition, while others fire low powered ammunition, including those designed for pistols.
AR15 - the Armalite AR-15 is a rifle that is almost identical to the M16 and M4. It is the civilian version of either (depending on the barrel length and collapsable stock) and comes in only semi-automatic capability.
Submachine Gun - an air-cooled, automatic carbine designed to shoot pistol cartridges.
Intermediate Cartridge - a firearm cartridge that is less powerful than a typical full battle rifle cartridge (7.62x51mm NATO, 7.62x54mmR) but still has a significantly longer effective range than a pistol cartridge. Examples include the 7.62x39mm, 5.56x45mm NATO, 5.45x39mm.
Gas Tubes and Hand Guards
There are 4 main lengths of M16 / AR-15 gas systems, which each require their own length gas tubes and hand guards, with different barrel lengths. The length of the gas system should increase as the barrel increases. This all has to do with “dwell time”, which is the time that the bullet spends in the barrel after the shot is fired.
On longer barrels, the dwell time will be longer as the bullet has to travel a longer distance down a longer barre.
Pistol Length - pistol length gas systems come on rifles with very short barrels, usually 10” or less. The gas tubes are approximately 4.5” and the hand guards are usually between 3” and 4” in length.
Carbine Length - one of the most common setups across all AR-15 rifles, with barrel lengths from 10” to 18”, the most common being 14.5”. The gas tubes are generally about 7.5” long.
Mid Length - mid length gas systems are very popular, and are commonly used with barrels from 14” to 20” long. They provide a longer sight radius, and reduce wear and tear on the upper receiver. The gas tubes are around 9.5” long.
Rifle Length - Rifle length gas tubes are generally about 13” long, and are found with 20” barrels or longer.
If you are unsure of which system you have, you can measure the length of your AR-15’s gas tube from the receiver to the gas block.
Some rifles have adjustable gas blocks, which allows you to increase or throttle down the amount of gas that travels through them. This is useful when either the rifle is so dirty that it needs more gas sent to the receiver, or when a suppressor is used, or to restrict the rifle to fire only single shot when firing grenades.
Article References: https://en.wikipedia.org/wiki/M4_carbine
https://en.wikipedia.org/wiki/M16_rifle
