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.
The M4 carbine is chambered for the 5.56x45mm NATO cartridge. It will also accept .223 Remington rounds.
If you mean the US Army, the M16 and the M4 variant of the M16.
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
14.5 inches on the actual M4 rifle.
The M4 is capable of automatic fire, the AR 15 is not
No one will give you an M4 rifle/carbine for free.
The .243. It's basically a necked down .308 Winchester.
The largest calibre i came across was 30 calibre russian rifle (gas chambers punctured to make it bolt action). owned by a retired army personnel. I guess they allow them to purchase it from the ordnance. Don't know if they can sell it though.
AR-15 = Semi-Auto civilian rifle M4 = Select Fire Military rifle
Not only the Army, but all the other service branches, as well as several law enforcement agencies (although theirs may have the government profile barrel, rather than the M4 profile barrel with the notch to accommodate the M203 or M320 grenade launcher). Not every Army unit uses the M4, or has it as the standard issue weapon - there are units in the Army where the M16 is standard, and the M4 may be reserved for support personnel, officers, etc.
20000
The M4 carbine has a muzzle velocity of 2,970fps(884m/s).