The rifle in "Blackhawk Down" is an M-14 that had a synthetic stock and an Aimpoint red dot sight mounted.
The M-14 replaced the M-1 (and also the M-1/M-2 carbines, BAR and the M-3 submachine gun) as the official US Military rifle in 1957 . It had a similar action to the M-1 but no parts are interchangeable. It used a 20-round detachable box magazine and fires the full power 7.62mm Nato round, identical to the .308 Win. round for all practical purposes and ballistically equal in military loads to the .30/06. The M-14 was capable of full automatic fire, unlike the M-1, but the selector switch was locked in the semiauto position on general issue rifles because the rifle was uncontrollable in full auto and the soldier's basic load of 100 rounds of ammo would be depleted too quickly. The M-14 has an integral scope mount base machined into the left side of the receiver.
The M-14 was replaced by the M-16 in the late 60's because of jungle fighting experience in Vietnam and the trend towards intermediate power "assault rifles". The M-16 is lighter, shorter, handier, recoils less and can be useful in full auto fire. The ammo is also lighter and today's basic load is 210 rounds, more than twice that of the M-14.
The navy continued using M-14's for many years onboard ship, and many M-14's were kept in storage. Modern desert and mountain warfare showed a need for the extra power and range of full powered battle rifles such as the M-14 and many were taken out of storage, refurbished and issued to special ops personnel, snipers and others who had a need to fight at long range or to be able to penetrate barriers, vehicles, etc.
The M-1A is the civilian version of the M-14 and is not capable of full automatic fire.
