Photo comparison of AR-10 and M-16 Rifles below

The old solid Armalite AR-10 30Caliber (7.62x51mm) Full-Automatic-Battle-Rifle (1960)
         Armalite AR-10 .30Caliber (7.62x51mm)
This old US Battle-Rifle is very solid & lightweight that can shoot accurately upto 700 meters. Tragically, it never saw action & never went into mass production. It is the predecessor of the M-16. This Rifle is also an excellent HUNTING RIFLE that can fire in Semi-Automatic and Full Automatic mode

Smaller & sleek Colts M-16 22Caliber (5.56x45mm) Assault Rifle (1969)
         Colt M-10 .22Caliber (5.56x45mm)
The M16 is the United States military designation for the AR-15 rifle adapted for semi-automatic, three-round burst and full-automatic fire. Colt purchased the rights to the AR-15 from ArmaLite. The rifle entered United States Army service and was deployed for jungle warfare operations in South Vietnam in 1963, becoming the U.S. military's standard service rifle 1969. As of 2010, the M16 is being phased out in the U.S. Army, and is being replaced by the M4 carbine, which is itself a shortened derivative of the M16A2