We start our study around 1948, right after the end of World War II. An official US Army historian, Colonel (later Brigadier General) S.L.A ("Slam") Marshall was beginning to study the effects of combat on men and eventually authored several books on the subject. One of the most well known books was titled Men Against Fire, in which he claimed that during World War II, when US soldiers who were engaged in direct combat, 75% of them never fired their weapon directly at an enemy even when they were in combat. Per his research, there appeared to be a deep reluctance to kill another human being even at the risk of being killed. While some of SLA Marshall's research methods and conclusions were questioned much later on, in the 1950s and 1960s, he could do no wrong and was regarded as the ultimate authority. Other studies by the US army showed that people armed with automatic weapons were more likely to fire them in combat, because they were less likely to think about the consequences of killing another human. Still other analysis by the US army determined that most infantry combat occurred at relatively close ranges and that the side with the most firepower tended to win most engagements. The number of casualties of the enemy was found to be directly proportional to the number of bullets fired.
All these studies pointed to the fact that infantry soldiers should be provided with automatic weapons. However, this meant that the soldiers would use up ammunition more rapidly and would need to carry more of it into combat. This meant that the size and weight of the ammunition would have to be reduced in order to avoid overburdening the soldier. A research team in the US Army's Aberdeen Proving Ground facility in Maryland, was tasked with researching the effects of smaller calibers. They found that a .223 caliber (5.56 mm.) bullet moving at higher velocities had the same effects as larger rifle rounds in many combat situations and requested further funding from the US military to perform more experiments.
At the time that the US army was experimenting with smaller calibers, a division of Fairchild Aviation called ArmaLite was formed in 1954, to investigate uses of new materials and new designs for the firearms industry. It was a very small company at that time and the ninth employee was a talented weapon designer and Marine, who had served during World War II, Mr. Eugene Stoner. They produced an innovative rifle for the 7.62x51 mm. NATO cartridge that was in use at that time, called the AR-10. The AR-10 had several new features that were later featured in the M16. It used a direct impingement gas-operated action, unlike other piston and cylinder driven firearms (such as the AK family) used at that time. The direct impingement action didn't have a moving piston and hence was lighter and easier to keep pointed on target, especially when firing in fully automatic mode. Another feature, which was borrowed from the German FG-42 and Johnson LMG was the idea of a straight-line stock (i.e. the rifle stock is in line with the barrel), which serves to reduce muzzle climb. Previously, rifles would have a bend in the stock, so that the sights would be at eye level, while the recoil could be transferred to the shoulder of the user. With the stock inline with the barrel, a lot of the muzzle climb is significantly reduced (read the article on muzzle-climb linked above for why) and therefore, Armalite increased the height of the sights to compensate and the rear sight was mounted as part of the carrying handle. The receiver was hinged (a feature also found on the FN FAL), but unlike most other rifles, it was constructed of aluminum alloy, which made it lighter than other rifles of its class. The bolt locking mechanism was also innovative for its time. The AR-10 was much lighter, smaller and easier to control in automatic fire than any of its competitors. However, against the wishes of Eugene Stoner, the president of Armalite wanted the barrel to also be made of aluminum/steel composite, which made the rifle's barrel weaker. Hence, when they submitted it for army evaluation, it burst under a torture test and was rejected. Armalite quickly replaced the barrel with an all-steel model, but the damage was done and the US army rejected the rifle. However, the improved model was used by a number of other forces around the world.
Meanwhile, a US general named Willard Wyman received the funding request from the Aberdeen Proving Ground facility and he formed a team to develop .223 caliber (5.56 mm.) firearms for testing. The finalized requirement asked for a firearm capable of selective fire, to be under 6 pounds (2.7 kg.) when loaded with 20 rounds. The bullet had to penetrate a standard US steel helmet of that time period from 500 yards, while exceeding the wounding properties of a .30 carbine. General Wyman had also seen the AR-10 trials and was impressed by some of its innovative features, so he personally asked Armalite to design a weapon using the 5.56 mm. cartridge. The result was a scaled down AR-10 model called the AR-15:
AR-15 assault rifle. Click on image to enlarge. Public domain image.
The AR-15 entered the design competition and the weird thing was that it entered with very little competition, because the main competitor (Springfield Arms) did not feel like diverting resources because they wanted to concentrate on M14 production, which the US military was already using. The only other competitor was an entry from Winchester called the LMR.
During the testing, it was found that rainwater could accumulate in the AR-15's barrel (as well as in the Winchester's barrel), due to the smaller diameter and capillary action. When such a rifle was fired, it could cause the barrel and action to burst. See myth #3 for the reason why. History buffs may also like to read a declassified report of the issue. The rifle was not as accurate in arctic conditions either. However, its lightness and rate of fire meant that an 8 man team could have the same firepower as a 11 man team using the M14 rifle.
In the next post, we will look into the adoption of the AR-15 and how it morphed into the M16