The M4 is an assault rifle based off it's popular cousins the M16 and AR 15 also assault rifles.
The M4 carbine fires NATO standard 5.56x45mm ammunition. This is often confused with commercial .223 Remington ammo, which is dimensionally similar. However, they are not the same.
In the related links box below, I posted the information.
For now, the M16 is supplemented by the M4 carbine version, but there is no replacement named as yet.
The M16 assault rifle has a greater range than the M4 carbine as a result of its 20-inch barrel, compared with 14.5 for the M4. The M16 can hit an area target out to 800 meters while the M4 is effective to 600 meters.
for a rifle it is thought to be a .50 calibre but a gun company made there own for there own sniper rifle the .408 calibre
MY Brand New Stag Arms M-4 Model #1 Cost me $850.00. I love it!
The M4 assault rifle has an overall length of approximately 33 inches (83.8 cm) with the stock fully extended, and its barrel length is about 14.5 inches (36.8 cm). It typically weighs around 6.36 pounds (2.88 kg) without any attachments or accessories.
14.5 inches on the actual M4 rifle.
The M16 is a gas operated, semi automatic assault rifle with a calibre of 5.56mm, used most commonly by U.S Forces and other countries.
The M4 carbine is a shorter and lighter variant of the M16A2 assault rifle. The M4 is a 5.56×45mm NATO, air-cooled, direct impingement gas-operated, magazine-fed carbine. It has a 14.5 in barrel and is 33 inches long.. It weighs 6.5 lbs.
The M4 is capable of automatic fire, the AR 15 is not