The M4 is capable of automatic fire, the AR 15 is not
AR-15 = Semi-Auto civilian rifle M4 = Select Fire Military rifle
AR 15 - semi-automatic only M16 - depending on variant capable of full auto or burst fire. Will also fire semi-auto.
No.
M4 is the carbine- shorter barrel
The US Army presently uses the M4 carbine, a shorter and much modified version of the Armalite AR15.
AR15, M16, M4, Ruger Mini 14
14.5 inches on the actual M4 rifle.
Law Enforcement
Both are assembly line weapons. Stag in my opinion also has a better reputation. Unless you decide to go tactical, they are all pretty much the same. Bushmaster, dpms, stag ext..
Their is no NATO M4. NATO countries that use the M4 either contract the purchase or license the production.
An M4A1 has semi and full auto capabilities, the M4 has semi and three shot burst capability, both are used by the modern U.S. Military. An M-14 is an infantry rifle used in Vietnam and Korea.
No one will give you an M4 rifle/carbine for free.