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:
locking system similar to Johnson Automatic Rifle
gas system from Swedish Ljungman AG42B
in-line stock to help with manageability during auto fire
hinged upper/lower from FN-FAL
rear sight in carry handle like British EM2
ejector port cover from MP44
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.
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funny how it goes. The AR15 was originally designed AND built by a CIVILIAN manufacturer whci in reality makes the AR15 a civliain firearm BEFORE it was a military firearm.
as for the "AR" well it was made by ARmalite. shouldn't be too hard to figure out should it?