Birth of the AR-15
In 1948, the U.S. Army established the Operations Research Office (ORO) to analytically study a number of problems associated with ground weapons in the nuclear era.
One of ORO's early projects was ALCLAD, a search for better infantry body armor. During this search, the ORO discovered just how little was known about how individuals were wounded in combat. ORO looked into several questions regarding the manner in which soldiers were struck by rifle projectiles and shell fragments, including:
Answers to these questions were obtained by evaluating over three million casualty reports for World Wars I and II, as well as data from the Korean conflict.
ORO's investigations revealed that in the overall picture, aimed fire did not seem to have any more important role in creating casualties than randomly fired shots. Marksmanship was not as important as volume. Fire was seldom effectively used beyond 300 meters due to terrain (WWII, Korea) although sharpshooters in WWI frequently saw 1200m shots, and it discovered that most kills occur at 100 meters or less.
From this data, ORO concluded that what the Army needed was a low recoil weapon firing a number of small projectiles so in 1957 the United States Army Continental Army Command (CONARC) sought commercial assistance in the development of a 5.56mm military rifle.
CONARC sponsored the development of a .22 military rifle and asked Winchester and Armalite to come up with designs for a high-velocity, full and semi auto fire, 20 shot magazine, 6lbs loaded, able to penetrate both sides of a standard Army helmet at 500 meters rifle. The competing rifles were:
The Armalite Division of the Fairchild Engine and Airplane Corporation, Costa Mesa, CA was established in 1954 for the sole purpose of developing military firearms using the latest in plastics and non-ferrous materials. It's team of Eugene M. Stoner - key designer, Robert Fremont - prototype manufacturing supervisor, and L. James Sullivan - who oversaw drafting work had been they key developers of the AR-15.
Prior to the AR-15, Armalite had developed:
AR-1 - 7.62 NATO parasniper rifle, extremely lightweight, using Mauser-type bolt action; only prototypes built in 1954
AR-3 - 7.62 NATO self-loader using aluminum receiver, fiberglass stock, and multiple lug locking system similar to the one later incorporated into the AR-10
AR-5 - .22 Hornet survival rifle developed for US Air Force and officially designated the MA-1
AR-7 - .22 long rifle self-loader, receiver and barrel store in plastic stock. (1959-1960)
AR-9 - 12 gauge self-loading shotgun with aluminum barrel and receiver (5lbs) 1955
AR-10 - 7.62 NATO auto-loader, aluminum receivers, led to AR-15 design
The AR-15, designed around slightly enlarged version of the .222 case firing a 55gr projectile at 3300fps, and weighing in at 6.7lbs, took some of the best features from earlier designs:
Project SALVO, a number of studies conducted by the Operations Research Office at Johns Hopkins University and supported by several contractors chose the AR-15 as the best small caliber weapon and it was adopted as the M16. The AR-15 had met all of the CONARC requirements, and AR-15 production could be highly automated, making it inexpensive to manufacture. It's 5.56mm cartridge fired a small 55gr bullet at nearly 3000fps, and it was accurate and effective to 350 yards. That small cartridge combined with the buffer system and inline stock made it far more controllable in automatic fire than the M14.