In the related links box below, I posted the information.
The M4 is an assault rifle based off it's popular cousins the M16 and AR 15 also assault rifles.
The M4 carbine is chambered for the 5.56x45mm NATO cartridge. It will also accept .223 Remington rounds.
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.
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 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
No such weapon, so no. However, there there is a M16A4. It is possible, but, highly unlikely that an individual can buy one.
No one will give you an M4 rifle/carbine for free.
The M4A1 is a variant of the M4 carbine, now capable of fully automatic fire. The M4 was in turn derived from the M16A2 assault rifle, which has rear sights adjustable for elevation and a brass deflector for left-handed users. The M4 and M16A2 share the same receiver and trigger group.